The jobs in highest demand in this field are petroleum engineers,geologists/geophysicists.And surprisingly,accountants.
Petroleum engineers are of the following types:
>reservoir engineers(find oil reserves and their economic viabilities,maximise output from wells,etc)
>production/industrial engineers(maintain quality of production from wells,linkages between wells and reservoirs,etc).
>drilling engineers ( to find best drilling methods to extract oil/gas in a particular region due to geological restraints)
Then you have the geologists and the geophysicists who assist the petroleum engineer in finding oil reserves,quality of oil that can be produced,problems that can be faced while drilling,geophysical properties of the drilling site,etc.
Accountants?Probably because of the rapid expansion in profits in this industry.
(comparison of job demand in oil/gas sector, 2011-2012)