In 1911, Saz Idemitsu established Idemitsu & Co. in Moji, northern Kyushu, to sell lubricating oil for Nippon Oil. In Shimonoseki, he began selling fuel oil for fishing boats.
In 1914, Idemitsu & Co. moved to Manchuria (China), where the Japanese-owned South Manchuria Railroad Co. Ltd. was a key lubricant customer. Idemitsu created a branch in Dalian, northeast China, in an attempt to break into the Chinese market, which was controlled by western businesses such as Standard Oil and Asiatic Petroleum Company (a Shell subsidiary). The corporation had a presence in northern China, as well as Korea and Taiwan.
The oil trade became government regulated after the Japanese invasion of Manchuria in 1932, and Idemitsu was obliged to cut it. Instead, he opted for oil tanker shipping.
The company’s headquarters were relocated to Tokyo in 1940, and the name was changed to Idemitsu Kosan K.K. (kabushiki kaisha: stock company). The government gained control of all industry as a result of Japan’s military expansion and the United States’ entry into the Pacific War.