JPMorgan downgrades Chevron, sees it as having the 'least upside' vs. competitors

Journalists are reflected in the sunglasses of drilling site manager Greg Murphy during a media day at Chevron's site in Pungesti, Romania, April 8, 2014.
Bogdan Cristel | Reuters

Chevron is now the "most expensive" energy stock after investors piled into the sector, according to JPMorgan.