(a) On casing-head gas used or sold for the manufacture of casing-head gasoline the minimum rate of royalty shall be 121⁄2 percent of the value of the casing-head gas, which value shall be determined and computed on the basis and in the manner provided in the applicable operating regulations of the Department.

(b) In cases where gas produced and sold has a value for drip gasoline, casing-head gasoline content, and as dry gas from which the casing-head gasoline has been extracted, then the royalties above provided shall be paid on all such values.