I've got my European Wildflower book here and you have a definitely either or.
You definitely have a buttercup - Ranunculus but then you knew that ;) If it has a bulbous base to the stem then you have Bulbous Buttercup - Ranunculus bulbosus, it it doesn't then you have a Meadow Buttercup - Ranunculus acris. If it has runners, then its Ranunculus repens (just read the other thread LOL) The flowers do look like they have a sheen on them and as children we would hold them under a friends chin, if the yellow reflected on the chin then we would say you like butter (kids ey!)
Either way they can be pretty agressive weeds, if you have a wildflower area then try and keep it confined there
This message was edited Thursday, Nov 15th 6:18 PM
Thank you Baa, for all your info and all the work looking this stuff up in your book. sounds like that book comes in pretty handy! I think I will keep a few in the wild flower bed for now, but I have learned the look so I can pull them out if they get out of hand.