(1)For the purposes of the duty there shall be for each oil field in each chargeable period an exempt allowance of 500,000 metric tonnes of oil divided between the participators in shares proportionate to their shares of the oil won and saved from the field during the period.
(2)If the gross profit accruing to a participator in a chargeable period from a field exceeds the cash equivalent of his share of the exempt allowance, the gross profit shall be reduced to an amount equal to the excess.
(3)If the gross profit accruing to a participator in a chargeable period from a field does not exceed the cash equivalent of his share of the exempt allowance, the gross profit shall be reduced to nil.
(4)Subject to subsection (5) below, the cash equivalent of a participator's share of the exempt allowance for an oil field for a chargeable period shall be equal to such proportion of the gross profit accruing to him from the field in that period (before any reduction under this section) as his share of the exempt allowance bears to his share, exclusive of excluded oil within the meaning of section 10 of the principal Act, of the oil won and saved from the field during the period.
(5)If a participator in an oil field so elects by notice in writing given to the Board at the time when he makes his return under paragraph 2 of Schedule 2 to the principal Act for a chargeable period, the cash equivalent of his share of the exempt allowance for the field for that period shall be determined under subsection (4) above—
(a)to the extent that his share of that exempt allowance does not exceed his share of the oil (other than gas) won and saved from the field in the period, as if in computing the gross profit accruing to him in the period all amounts relating to gas fell to be disregarded ; and
(b)to the extent, if any, that his share of that allowance exceeds his share of the oil (other than gas) so won and saved, as if in computing the gross profit so accruing all amounts relating to oil other than gas fell to be disregarded.
(6)In this section references to a participator's share of the oil won and saved from a field are to his share as expressed in metric tonnes and for that purpose 1,100 cubic metres of oil consisting of gas at a temperature of 15 degrees centigrade and pressure of one atmosphere shall be counted as equivalent to one metric tonne of oil other than gas.