The data on international crude oil trade is downloaded from UN Comtrade, which contains crude oil
export and import flows among 181 countries in the world. We selected the annual crude oil trade data for
all these countries from 1993 to 2012. We represented countries as nodes and trade relations between
countries as edges. The directions of the edges are the directions of crude oil trade flows, and the weights
of the edges are the trade volume of crude oil measured by tons.