delivered the opinion of the Court.
The question is whether a state statute imposing a privilege tax on the production of mechanical power contravenes the interstate commerce clause in so far as it is applied to an engine used to supply mechanical power to a compressor which increases the pressure of natural gas and thus.permits it to be transported to purchasers in other states.
Act No. 6- of the Regular Session of 1932 of the Louisiana Legislature, with certain qualifications and exceptions not material here, provides for a license tax to be paid by everyone engaged within the State in the business of manufacturing or generating electricity for heat, light or power, § 1, or of selling electricity not manufactured or generated by him or it, § 2. Section 3 provides that every person, firm, corporation, or association, engaged within the State in any business, which uses in the conduct of *606 that business electrical or mechanical power of more than ten horsepower and does not procure all the power from a taxpayer subject to § 1 or § 2, “shall be subject to the payment of an excise, license, or privilege tax of One Dollar ($1.00) per annum for each horsepower of capacity of the machinery or apparatus, known as the ‘prime mover’ or ‘prime movers,’ operated by such person, firm, corporation or association of persons, for the purpose of producing power for use in the conduct of such business or occupation; . . .”
Appellee is engaged within Louisiana, Arkansas, and Texas, in the business оf producing and buying, transporting and selling natural gas. The gas is obtained from the Monroe and Richland fields in Louisiana, and transported through appellee’s 20-inch pipe line, one of the largest in the Southwest, which extends from Ster-lington, Louisiana, to Blanchard, Louisiana, where one branch goes west into Texas, and the othеr north into Texasi and Arkansas up to Little Rock. Ninety-six and 6/10 per cent. (96.6%) of the gas transported through this line during the fiscal year ended July 31, 1933, was delivered outside the State of Louisiana.
The natural gas cannot be transmitted through this pipe line for these distances in amounts sufficient to meet the needs of appellee’s custоmers, unless it is delivered into the pipe line at a pressure higher than that at which it comes from the wells. Accordingly, appel-lee maintains in Louisiana, at the point of intake into the line, its “Munce Compressor Station” where are located ten pumps, or natural gas compressors, which operate to increase the pressure of the gas to the required extent. These compressors are directly connected to ten four-cylinder 1,000 horsepower Cooper Bessemer internal combustion gas burning engines. There are also two 250 horsepower gas burning engines for general power service at the station. Thе tax is laid on the privilege *607 of operating these twelve gas engines, known as “prime movers,” 1 and is imposed at the rate of $1 per horsepower capacity of the engine—i. e., a total tax of $10,500.
Appellee’s complaint, setting forth these facts, was filed in the District Court for Western Louisiana. It prayed that the tax be declared invalid and that the appellant, sheriff, be enjoined from selling appellee’s property to enforce payment of $7,316, plus certain penalties and attorney fees, as the balance of the “prime mover tax” due for the year ending July 31, 1933.
2
An
ex parte
temporary restraining order was issued. A statutory three-judge court was convened, and a preliminary injunction granted,
First.
The character of the tax act under consideration is clear. It is a revenue measure obtaining funds by levying a privilege tax on those generating or selling electricity in Louisiana. §§ 1 and 2. Prеsumably to protect this source of revenue against tax-free competition, § 3,
4
with
*609
broad exemptions not assailed here, subjects the users of electrical or mechanical power, not procured from those subject to § 1 or § 2, to a tax of one dollar per annum for each horsepower оf capacity of the machinery operated by the taxpayer for the purpose of producing this power. The state court has held that section three, here in question, does not lay a tax on those who .own the machines but on those who use them in the conduct of their business,
State
v.
H. L. Hunt, Inc.,
Second.
The language of the state statute makes it quite certain that this privilege tax falls alike on those engaged in interstate оr in intrastate commerce, or in both. While a privilege tax by a state for engaging in interstate business has frequently met the condemnation of this Court as a regulation of commerce,
5
privilege taxes
*610
for “carrying on a local business,” even though measured by interstate business, have been sustained.
American Mfg. Co.
v.
St. Louis,
Taxation by the states of the business of interstate commerce is forbidden only because it is deemed an interference with that commerce, the uniform regulation of which is necessarily reserved to the Congress.
Minnesota Rate Cases,
Privileges closely connected with the commerce may be regarded as distinct for purposes of taxation. So, local privilege taxes on storage in transit, compressing or dealing in cotton, already moving in its intеrstate journey from plantation to mill, are validated as imposed upon operations in connection with a commodity withdrawn from the transportation movement.
Federal Compress Co.
v.
McLean,
The power used by the appellee is obtained from internal combustion engines which transform the potential energy of natural gas into mechanical power, transmitted by piston and piston-rod from the combustion chamber of the engine to the compression chamber of the compressor. While the engine and compressor units are assembled on a common bed plate, their functions are thus seen to be as completely separate as if they operated through belting. The engine is the “prime mover” of the tax act, producing power to drive the compressor. While the use of the engine for the production of power synchronizes with the transmission of that power to the compressor, production occurs prior to transmission. It is just as much local as the generation of electrical power.
Helson
v.
Kentucky,
Third.
To determine whether this challenged state tax enactment is invalid as an interference with interstate commerce under the decisions of this Court, the connection of the privilege taxed with interstate commerce has been considered. Other factors also show that the tax here does not interfere with interstate commerce. The tax is without discrimination in form or application as between inter- and intra-state commerce and it cannot be imposed by more than one state. The course of interstate commerce is clogged by taxes designed or applied so as to hamper its free flow. Section three, however, bearing equally on all use, is оnly complementary to the taxes of sections one and two.
Henneford
v.
Silas Mason Co.,
It was held by the Distriсt Court that this is a tax which may be levied by other states and so is invalid, and that a state’s desire to save gas- for its citizens may induce it to raise the privilege tax to prohibitory rates. It is true that each state through which a pipe line passes could lay a tax on the use of engines for the production of power, but that wоuld not be multiple taxation *613 “merely because interstate commerce is being done,” as discussed in Western Live Stock v. Bureau of Revenue, ante, p. 255, and the authorities there cited. It would not be a tax on the same activity, either in form or in substance. Like a property tax on the pipes or equipment in different states, it would be a different tax, on a different and whоlly separate subject matter, with no cumulative effect caused by the interstate character of the business. It would not be multiple taxation for each state to tax the “booster station” ad valorem as property. Neither is it prohibited multiple taxation to have the possibility of other privilege taxes on the produсtion of power. It is length of line, not interstate commerce, which makes another tax possible.
The decree of the District Court is
Reversed.
Notes
This term, used in § 3, supra, is not defined elsewhere in the statute. Webster’s New Intеrnational Dictionary (2d ed. unabridged, 1936) p. 1964, contains the following: “prime mover. Mech. . . . h An initial source of motive power, as an engine, or machine, the object of which is to receive and modify force and motion as supplied by some natural source, and apply them to drive other machinery, as a water wheel, а water-pressure engine, a wind-mill, a turbine, a tidal motor, a steam engine or other heat engine, etc.” As explained by expert witnesses for the appellant, the internal combustion gas engine is a prime mover which converts heat energy, contained in the natural gas as fuel, into mechanical energy, then supрlied to and used by the compressor unit.
Appellee alleged that it had paid part of the tax imposed by the statute in order to avoid a forced sale.
The first opinion also held the statute invalid in its entirety (on the authority of
Union Sulphur Co.
v.
Reid,
“Section 3. In addition to all other taxes of every kind imposed by law, every person, firm, corporation or association of persons engaged in the State of Lоuisiana in any business or occupation, which person, firm, corporation or association of persons uses in the conduct of such business or occupation, at any time, electrical or mechanical power of more than ten horsepower and does not procure all the power rеquired in the conduct of such business or occupation from a person, firm, corporation or association of persons subject to the tax imposed by Section 1 or Section 2 of this act, shall be subject to the payment of an excise, license or privilege tax of One Dollar ($1.00) per annum for eaсh horsepower of capacity of the machinery or apparatus, known as the 'prime mover’ or 'prime movers’, operated by such person, firm, corporation or association of persons, for the purpose of producing power for use in the conduct of such business or occupаtion; provided that any user of power securing all or any part of the power required in the conduct of the business or occupation of such user from a person, firm, corporation or association of persons subject to the tax imposed by Section 1 or Section 2 of this act, shall not be liable fоr the tax imposed by this Section 3, or for a greater tax under this Section 3, as the case may be, because of the employment of stand-by power facilities by such user during periods of failure of the supply of purchased power; and provided further that any person, firm, corporation or association оf persons the principal use of whose electric facilities is the generation of electricity for sale, shall not be subject to an additional tax under *609 this Section 3 on the horsepower capacity of any machinery or apparatus used in the generation of electricity; and provided further that in computing the tax imposed by this Section 3, there shall be excluded from the horsepower capacity of all machinery and apparatus operated, that part of such capacity used in a mechanical, agricultural or horticultural pursuit, or any other occupation exempt from a license tax under Section 8 of Article X of the Constitution of Louisiana, or in operating a sawmill or a mill for grinding sugarcane or producing raw sugar, or in conducting any business of selling electricity or any business conducted under any franchise or permit granted by the State of Louisiana or any subdivision thereof, or in propelling or motivating any automobile, truck, tug, vessel, or other self-propelled vehicle, on land, water or air.”
Cooney
v.
Mountain States Tel. Co.,
But see
Crew Levick Co.
v.
Pennsylvania,
