A tax, to be known as petroleum revenue tax, shall be charged in accordance with this Part of this Act in respect of profits from oil won under the authority of a licence granted under either the [1934 c. 36.] Petroleum (Production) Act 1934 or the [1964 c. 28 (N.I.).] Petroleum (Production) Act (Northern Ireland) 1964; and in this Part of this Act " oil" means any substance so won or capable of being so won other than methane gas won in the course of operations for making and keeping mines safe.

For each oil field the tax shall, in the case of each participator, be charged at the rate of 45 per cent, on the assessable profit accruing to him in any chargeable period from that field, as reduced under section 7 of this Act by any allowable losses and under section 8 of this Act by reference to his share, if any, of the oil allowance for that period, subject however to the limit imposed in his case by section 9 of this Act.

In this section—

• " the critical half year ", in relation to an oil field, means the first half year ending after 12th November 1974 at the end of which the total amount of oil ever won and saved from the field exceeds 1,000 long tons (counting 40,000 cubic feet of gas at a temperature of 15 degrees centigrade and pressure of one atmosphere as equivalent to one long ton);

• " half year " means a period of six months ending at the end of June or December.

Schedule 1 to this Act shall have effect with respect to the determination of oil fields, and Schedule 2 to this Act shall have effect with respect to the management and collection of the tax; and this Part of this Act shall have effect subject to the further provisions in Schedule 3 to this Act and, in connection with certain gas sold to the British Gas Corporation, to section 10 of this Act.