It's a pipeline war, although some would disagree. The Yemeni regime is aligned with or sympathetic to Iran.
Given that Straight of Hormuz is the largest oil chokepoint in the world, and necessary for Saudi crude, as they do not presently have enough pipeline capacity. As of 2013, seventeen million barrels transit through the Straight each day. This is about 19% of total world supply. The Iranians have been practicing a blockade of the Strait for many years.
Aside from Yanbu terminal on the Red Sea (1.3 million bbl/d capacity), two of Saudi Arabia's largest oil export terminals -- Ras Tanura and Ras al-Ju'aymah -- are in the Persian Gulf. Between the two, they represent an average daily capacity of 6.4 million bbl/d.
According to a Wikileaks cable:
Oil and the Yemeni Succession
- (C) A British diplomat based in Yemen told PolOff that Saudi Arabia had an interest to build a pipeline, wholly owned, operated and protected by Saudi Arabia, through Hadramaut to a port on the Gulf of Aden, thereby bypassing the Arabian Gulf/Persian Gulf and the straits of Hormuz. Saleh has always opposed this. The diplomat contended that Saudi Arabia, through supporting Yemeni military leadership, paying for the loyalty of shaykhs and other means, was positioning itself to ensure it would, for the right price, obtain the rights for this pipeline from Saleh's successor.
Opponents to this theory claim the timeline of events doesn't make sense, but the counterargument, as claimed, is interest in bypassing the Straight of Hormuz has been of strategic interest for decades.
