Almost all fuel sold in the US is produced domestically, with a limited amount of gasoline and diesel imports supplementing regional markets. The US mainland is split into five distinct supply areas known as Petroleum Administration for Defense Districts (PADDs). Federal Renewable Fuels Standard and state-level Low Carbon Fuel Standards are driving an increasing share of biofuels in road transport. However, biofuel volumes decline from the mid-2030s as road fuel demand wanes due to vehicle electrification. Similar to some other mature markets, there is a strong presence of convenience store operators in the retail fuel market. These players often adopt a high volume, low margin model with the sale of higher margin non-fuel items offsetting the slim margins generated from fuel sales. Although the brands of the major oil companies and refiners are widely present at forecourts across the country, very few sites are owned or operated by these companies.