“ Am I able to claim per diem and/or mileage in this situation?”---->In general negative; since you principal work place is 99 miles away from your residnece, where you work is your tax home(which you live on near the rig). Unfortunately not much will be deductible. For example, as you can see, even general mileage going to and from work is called commuting and is not deductible; every employee has to go to work.If you use your vehicle while you are at work for business purposes then it will be deductible, but this is not your case. Your safety equipment and clothing not suitable for wear on the street would be deductible. Your job related union dues payables would be deductible. If your work was not your tax home the answers would be different. Examples are truck drivers that are in a different place everyday or carpenters who travel to different job sites away from home.