We plan to take the RER from St. Michel ND to Versailles on a Saturday and had planned to buy a roundtrip ticket. Not knowing how long we may spend at the chateau I was thinking that on the way back to Paris if it is the afternoon and we are still interested in more sightseeing would we be able to get off at any on the stops along the way, for example Champ de mars and if we did, could we get on a few hours later at the same stop and continue on to St. Michel ND without having to buy another ticket? I'm assuming once we leave the RER any where along the line we would need another ticket to continue back. I am talking about individual tickets and none of the passes. Thanks!

Your answers can be found on the English version of www.ratp.com

just buy a day pass.

To answer your question . . .

No, if you leave the station at Champ de Mars, you will have to buy a regular metro ticket to go from there to St. Michel ND later (or walk, cab, bus, batobus).

Thanks so much for the info-I had researched the ratp site extensively and wasn't sure if the RER fare to Versilles could be used like the regular tickets where they talk about the 2 hour limit. Someones personal experience is always helpful!!