This is a fairly standard cycle that is noted in O&G. Oil goes down when the supply gets too large. When this happens many large companies need to cut production and this means massive layoffs. As this happens the supplies slowly dwindle down and in turn eventually the demand gets high again and price begins to rise. As this prices rises production at places resume or new site are now viable, resulting in a mass hiring and over supply eventually again. Now we hit where I started and it begins all over.

(although the sitation may be a bit different than previous decades through the now common horizontal drilling and fracking techniques being used (mostly in america) and the eastern countries flooding the market with their cheap oil to hurt western producers)