As I understand it, a large percentage of Japanese oil was imported from the US in the pre-war years. As a consequence of their actions in China, the US cut off oil exports to Japan. Thus, with such a large percentage of their oil supply gone, what motivated them to start the war on the US, increasing consumption of an already threatened resource? Did they hope to conquer an oil rich area in the United States? Were they working toward an oil-rich area of China that would allow them enough supply to fight both the war in China and the US? Did signing on with the Axis powers alleviate Japanese oil issues at all?
Edit: I'm on my second listen-through of Dan Carlin's Supernova in the East. Though he goes into the pre-war oil situation a bit in II, there's nothing about Japanese motivations in regards to oil supply and attacking the US. Only that the lack of US exports of oil was a contributing factor to Japans desire for war. Nothing about how said war would alleviate Japanese oil issues, thus my curiosity.
The Japanese sought their oil primarily from the Dutch East Indies. Full answer:
First, the American oil embargo was a response to Japan moving into Indochina (present-day Vietnam, Laos, and Cambodia). Ongoing Japanese military operations in China had put a strain on the US-Japan relationship and were part of the problem, but the two events that are usually remembered as "oil embargoes" came after Japan moved into Indochina. The United State cut off aviation fuel exports following Japan's occupation of northern Indochina in 1940. In summer 1941, the Japanese expanded again into southern Indochina and the U.S. responded with a de facto embargo of all oil exports, though that may not have been the original intent (see the linked answer above).
The Japanese never sought to invade the U.S. mainland for oil and never came remotely close to having the capability to do so. In fact, the Japanese never even had the capability to invade Hawaii, and never seriously considered doing so.
I'm not an expert on the Sino-Japanese War, unfortunately. I don't believe there were any significant oil deposits in the areas of China that the Japanese were fighting, however. Japan's relationship with Germany and Italy neither helped nor hindered its supply of oil, though it did create further issues in their bilateral relationship with the Americans.
The Japanese had a reserve of oil that had been set aside that would provide for enough to execute their war plans. However, once the Americans cut off oil exports in summer 1941, that reserve began to dwindle. The Japanese war machine in China continued to consume oil and other raw materials, as did the civilian economy. A large-scale naval offensive would increase Japan's oil consumption, as would the training that led up to the start of the war.
Japan sought secure oil fields in the Dutch East Indies (present-day Indonesia and Brunei). American negotiators warned the Japanese that a move against the Dutch East Indies was not acceptable to the United States. The Japanese considered whether they could seize the Dutch East Indies and other areas they sought to control without starting a war with the Americans. However, the large American military presence on the Philippines could not be overlooked. If the Americans held the Philippines, they had a large base of operations for warships and aircraft that could interdict Japanese supply lines from the Dutch East Indies and elsewhere in Southeast Asia. The American Pacific fleet, by then anchored at Pearl Harbor, also posed a threat. The Japanese examined whether they could bypass the Philippines and hope to avoid war with the Americans, but (probably correctly) determined it was not possible. The Americans would have to be dealt with to secure Japan's position in the Pacific.
The Japanese oil reserve had enough for the Japanese to start the offensive and hopefully secure the oil fields in the Dutch East Indies (which they did), but they needed to keep that supply line open to continue to draw resources from the area. The American submarine campaign during the Pacific War was instrumental in breaking the Japanese economy by cutting off several vital imports into the Japanese economy, with oil being one of the most critical.