The HD on which Oblivion was installed failed. Saves were on another HD. When I reinstall Oblivion on a new HD, how can I determine from a save file which mods I need to reinstall to continue the game from that save or which mods were active when the game was saved?

You can use OBMM or Wrye Bash to find out saved master list.

Doesn't the masters list that Bash produces include only the mods that supply resources that other mods require rather than showing all mods that were active?

Click on the Saves tab in Wrye Bash and click on a save file to see all mods active during that save.

Thanks. I'll try that when my new HD arrives in about a week. I'm just hoping I have no major problems with the reinstallation.

They will only show active mods, so any mods merged into a bashed patch will not show.

Also, you'll only get a list of esp's. If you installed anything that was just mesh or texture replacement, it won't always show up anywhere. On the other hand, the save game will work without those, it will just look different!