To my understanding the United States was the largest exporter of oil to the Japanese prior to Pearl Harbor. The Japanese islands aren't known for their oil fields. It's also believed that the attacks of pearl harbor are the result of the US refusing to send Japan oil. Were there any other countries supporting Japan with oil?
How did the Japanese manage to maintain a military without imported oil?
Japan had a small domestic oil production, a few million barrels, but not nearly enough to meet their peacetime needs let alone war. What they did have is enough oil refineries with a capacity of almost a year's peacetime consumption. If they could get the oil to Japan, they could refine it into fuel. They were also heavily invested in synthetic oil plants to convert coal, tar and shale into oil. Even sugar, rice, nuts and pine were converted to oil.
Before the war started, they imported 90% of their oil, mostly from the US. The US produced the majority of the world's oil in 1941, a lot of it in California. Not having the infrastructure to ship it across the US, it was loaded onto tankers and sold around the Pacific Rim. Months before the war began this supply was cut off by a US embargo, later joined by the Dutch. By threatening the US and the Dutch they cut off their oil supply.
Japan also had a stockpile of oil and other strategic resources, billions of barrels. Roughly equal to two years of peacetime imports. They would need it.
Japan imported most of its oil from conquered territories, primarily the Dutch East Indies (aka Indonesia) but also smaller amounts came from Formosa (Taiwan), China, and Burma. Many of these plants and fields were damaged by their defenders and it took years to get them back to near full production. Japan also had a concession from the USSR to mine on Sakhalin Island which continued to be honored, though the amount of oil was very small. But it never was enough. Without US oil, their imports were slashed in half.
All that oil had to be shipped to refineries and the products to where it was needed by an ill-defended merchant fleet. Japan would be further crippled by the loss of most of this fleet to American and Allied submarines, aircraft and mines.
The Navy was a huge consumer of oil, needing a billion barrels of heavy oil a year. Military and civilians needed half a billion barrels of diesel. Aviation took another half billion barrels. As oil imports plummeted and stockpiles were depleted, the heavy units of the Japanese navy were more and more often confined to port and their aircraft grounded. Training programs were cut, the fuel could not be afforded for the hours necessary to train pilots and crew, and the initially high quality of Japanese naval personal and pilots plummeted.
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The USSR also continued trading oil with Japan? This part is surprising if you take into account the devastating effect of WWII on USSR. Actually, United States transferred more than 2 million tons of petroleum to the Soviet Union.
Commented
Nov 11, 2015 at 6:28
Japan had stored up enough oil for one year's worth of war. When the United States (Japan's main supplier), imposed an embargo on oil (and other goods) in July, 1941, Japan had to do something.
That "something" consisted of two parts: 1) a "first strike" at Pearl Harbor to cripple the U.S. fleet and 2) an invasion of Southeast Asia, that was the key to most of the oil Japan used for the duration of the war.
http://www.mapsofworld.com/asia/regions/south-eastern-asia-map.html http://www.mapsofworld.com/asia/regions/south-eastern-asia-map.html
This included the Hong Kong, Philippines and Indochina, then Singapore, the Dutch East Indies, and "island" Malaysia, at the southern part of the map (specifically the islands of Borneo and Sumatra). The latter three areas were a great source of oil (or refineries, in the case of Singapore).
Japan got a little bit of oil from Manchuria, and Siberian Russia (a neutral country), but not nearly enough.
