Dress code for field based engineers

Can anyone tell me what the normal day-to-day dress code is for engineers based in the oil field?
For example is it jeans and polo shirt or slacks and short-sleeved dress-type shirt (or shorts and flip-flops)?

first suggestion

Is that a general rule everywhere, or is office work in the city normally shirt and tie.

in most cases, u need to wear the safety gear if your on the job location or rig, but to drive there, u will be fine with jeans and polo.

however, if you were working in the office for an oil company, casual is okay and acceptable.