In the United States, about 425 million oil filters are sold each year as of 2015. People who change their own oil account for about half of these sales, while the rest go to automotive shops.
Oil enters the filter under pressure through holes all around the base plate. The oil then goes through a filtration process to clean out impurities. After passing through a central tube, it returns to the oil passage through the engine. The pressure ranges from 5 to 100 PSI depending on the design and type of the engine, and most engines pump oil at a rate of more than a gallon per minute.