I will try and add comments and insights into this industry. I have worked in the oilfield since 1996 and have had many experiences and met many interesting people.
I will list the various job titles, so as to avoid confusion later.
This blog will include land based and offshore experiences!

Roustabout - works on the deck (away from rig floor)
Roughneck - works on the rig floor
Derrickman - works high in the derrick, also in charge of mud mixing system
Assistant driller - job description says it all
Driller - drills the holes!
Night Toolpusher - basically in charge at night
Senior Toolpusher - in charge during the day
Company man - thinks he is God! In charge for the oil company and all the other jobs above are for the drilling contractor.

Drilling contractors own the rigs and Oil companies hire them for a fixed day rate and the Drilling contractor then operates the rig for the Oil Company.