Jennifer, I work in software development for a geophysical data processing company that processes seismic and oil/gas well data, refines it, then sells it to the oil and gas companies that are interested in it. Thus far my company has been 100% behind me. Also, I had spoken to some people and several of the mid-size O&G companies in Houston appear to be trans friendly too, like Hess, Andarko, and others.
About the only one of the "big" oil companies that I consistently hear bad things about is Exxon and they apparently have LGBT issues across the board within management there. But as one executive remarked to me, it's their loss as the rest of us get some top notch folks who just won't even apply to work there.