I work in the oil field and I drive a company vehicle from my home to the office and then to the field. Coming home I usually go straight home from the field other times I go by the office. My employer recently changed our policy they will pay time from the office to the field but have said once we are on the pavement going home we are no longer on the clock, "we drive home on our own time". It is between 1.5 to 2hrs to the field where I get on/off the pavement. Is this legal, and if it is if I leave my truck at the office would they have to pay me both ways?

This is potentially complicated. There is a 1940s law called the Portal-to-Portal act that says that commuting is not hours worked. There are some exceptions but the law's clear intent is that the employer does not have to pay for commuting time. It is not legally the employer's responsibility that you have a long commute. The 3-way commute aspect (work site, office, home) is more complicated. If your employer is telling you to report first to the office, then the "clock" starts there. If instead you are the one deciding that "if I leave my truck at the office would they have to pay me both ways", then they do not have to pay for the office-worksite portion.

The related regulations are 29 CFR 785.33-785.41. You really need to read everything in that group. Picking out a specific regulation that seems to say what you want does not help if the next regulation says something else.

http://www.dol.gov/dol/allcfr/ESA/Title_29/Part_785/29CFR785.33.htm

Thank you,
I do have one other question that is in regards to your statement "It is not legally the employer's responsibility that you have a long commute." The length of my commute is determined by what field I am assigned to work in. Some are in town and then they progressively get farther and farther from town. Which field I am assigned is determined by my employer. It changes from time to time maybe yearly, so for a while it may be 10min then it changes to 2hrs. Moving closer to the field is not an option because there is no housing close to it. Would that make a difference?

Maybe. You need to read the actual regulations I cited. If you are asking if based on what you said so far that your employer must pay more money, then the answer is no. If instead based on what you did say and also based on other facts not yet stated, then maybe possibly the employer owes more money.

The key is that since the Portal-to-Portal act very specifically says that commuting is not time worked. Your only recourse is to read those very specific regulations I have cited and find very specific facts that support the exception. So far, nothing you have said (by itself) has done that.

I will do that thank you for your help