There are four main types of motor oil: conventional, synthetic, synthetic blend, and high-mileage oil. Conventional oil is the most affordable but requires more frequent changes around every 3,000-5,000 miles. Synthetic oil provides better protection and performance and can be changed less often at around 10,000 miles. Synthetic blend oil offers benefits of both conventional and synthetic at a lower cost, needing changes every 7,500 miles. High-mileage oil is suited for older vehicles with over 75,000 miles to reduce leaks and consumption.