Up until 2017, the US was the main importer of oil products across the world, however as the US domestic capacity has grown and consumption declined, their reliance on imports has diminished to the point where China has now become the largest importer of oil (see chart below)
The issue for China is that since 1973, Saudi Arabia agreed to price its oil only in U.S. Dollars, and store their petrodollar revenue in U.S. Treasuries, thereby financing U.S. Debt. OPEC followed suite in 1975. In exchange, the US would ensure the continuity of the ruling house of Saud, providing military protection and American weaponry. The strength of this agreement has been waning for years and the geopolitical games that are at play through the middle east all part of the mess that follows.