The us imports roughly 9% of its petroleum from SA, (it's second largest single-source after Canada)[0], which is significant. However, I think if you polled policy makers they'd emphasize security interests over oil. SA serves as a powerful Sunni counter-balance to the largely Shiite Iran. They are huge purchasers of western arms, and often (explicitly) support western interventions.
[0] https://www.eia.gov/tools/faqs/faq.php?id=727&t=6