Does anyone one have a gentle method of removing glass stoppers? [View all]

I have a small decanter that might be a good piece of glass. My husband bought it over 10 years ago, and the stopper was stuck then. We tried different suggestions to get the stopper out at the time, and nothing worked. I even thought maybe the stopper wasn't meant to come out. We stopped trying, and it has been on the shelf since then.

I took it from the shelf today, and dabbed some olive oil around the rim of the stopper. I'll let it sit for awhile. When we got it, we tried heating the decanter and cooling the stopper, didn't help. Too long ago to remember what else we tried. I'd rather keep it stuck than break it. If anyone has any tricks, I'd appreciate hearing them. Thank you!