Just food for thought, but it is possible that the sweating isn't weight related. An antidepressant that I was on for years (at weights ranging as low as 120) gave me horrible night sweats, and during the day my thighs would sweat while sitting in exactly the way you described.
I didn't even connect the sweating with the meds until I stopped taking them and the sweating stopped abruptly!

That is definitely a good thought, but I'm not taking any medication. I wonder what it could be. I mean the rest of me is fine, it's just the back of my thighs. What's a good clinical strength deodorant?

I like the Secret Clinical Strength deodorant. It's pretty pricey (about $8 per tube), but it's awesome stuff.

I found a website that described your condition and listed possible reasons for it and some ways to help it....

the name of the problem is compensatory hyperhidrosis

Hey there, just popping in to say I have that too. But my legs primarily sweat around the inner thighs and around the butt. However my most embarassing sweating occurs on my back. I have serious back sweat when I walk in hot weather (and worse if i wear a back pack). I actually have to bring another shirt to change into. I sweat under my boobs too, but I can handle that. It's the back sweat that gets me. :(

I totally sweat when I'm sitting down on hard chairs. The back of my thighs sweat alot. When I get up from wooden chairs, it leaves white marks on the chair and my pants are damp. I usually wear jeans. I hate it. I think I'll try the Gold Bond powder. It's so embarassing. :o
Amy

I use Gold Bond everywhere the smell doesn't seem to linger. Also do you wear Cotton underwear if I wear anything else I sweat really bad.

Thank you for your input. I really appreciate it. It's cool that this happens to other people too. I will try the Gold powder to see if that helps. I'm willing to try almost anything.