How to Oembed a Vimeo video and have it automatically size responsively?

I need to embed Vimeo videos using Oembed (not using the iframe code), and of course they need to size responsively, as YouTube videos do automatically. Can you recommend a good way to do it? I tried the 2 best-rated WP plugins (Fluid Video Embeds and Responsive Video Embeds), and they had no effect at all. Using WP 3.8 and a “premium” theme called “Sans”.

I can provide a URL on request but can’t leave it open indefinitely.

Thank you very much in advance!

Best,

Patty Ayers