The lessee shall pay, beginning with the date of approval of oil and gas leases by the Secretary of the Interior, a rental of $1.25 per acre per annum in advance during the continuance thereof, together with a royalty of 12 1/2 percent of the value or amount of all oil, gas and/or natural gasoline, and/or all other hydrocarbon substances produced and saved from the land leased, save and except oil and/or gas used by the lessee for development and operation purposes on the lease, which oil or gas shall be royalty free. A higher rate of royalty may be fixed by the Secretary of the Interior or his authorized representative, prior to the advertisement of land for oil and gas leases. During the period of supervision, “value” for the purposes of the lease may, in the discretion of the Secretary of the Interior be calculated on the basis of the highest price paid or offered (whether calculated on the basis of short or actual volume) at the time of production for the major portion of the oil of the same gravity, and gas, and/or natural gasoline, and/or all other hydrocarbon substances produced and sold from the field where the leased lands are situated, and the actual volume of the marketable product less the content of foreign substances as determined by the supervisor. The actual amount realized by the lessee from the sale of said products may, in the discretion of the Secretary of the Interior, be deemed mere evidence of or conclusive evidence of such value. When paid in value, such royalties shall be due and payable monthly at such time as the lease provides; when royalty on oil produced is paid in kind, such royalty oil shall be delivered in tanks provided by the lessee on the premises where produced without cost to the lessor unless otherwise agreed to by the parties thereto, at such time as may be required by the lessor. The lessee shall not be required to hold such royalty oil in storage longer than 30 days after the end of the calendar month in which said oil is produced. The lessee shall be in no manner responsible or held liable for loss or destruction of such oil in storage by causes beyond his control.