Cal. Business and Professions Code - BPC § 13520. Section 13520.
It is unlawful for any distributor or for any broker to sell any product to a retailer or to any person, when the quantity distributed in any single delivery to a single location is 5,000 or more gallons, as, or purporting to be, gasoline or diesel fuel, unless the distributor or broker, as the case may be, offers to invoice the purchaser for such gasoline or diesel fuel on the basis of temperature-corrected gallonage to 60 degrees Fahrenheit for all such deliveries to the purchaser over a period of 12 consecutive months and settles his accounts with the purchaser on the same basis.