According to Jack Bruce's 'British Aeroplanes 1914-1918', page 589, the tankage is - Petrol: main (pressure) tank, 30 gallons; gravity tank, 7 gallons; total 37 gallons. Oil: 6 1/2 gallons. (all imperial).
However, in the weights section the weight of the fuel and oil can differ between differently engined Camels, as does endurance so there was some variation.