Reese Witherspoon & Oliver Haarmann Pack on PDA on Yacht in Saint-Tropez

Reese Witherspoon's sailing the French Riviera this summer on a luxury yacht with her boyfriend Oliver Haarmann ... and if that doesn't sound romantic enough, check out these photos of Reese and Oliver smooching like there's no tomorrow.

The actress and her financier boyfriend packed on the PDA Sunday in Saint-Tropez ... locking lips and getting handsy on the stern of their big fancy boat.

Reese and Oliver kissed, hugged, laughed and embraced as they sat with their feet dangling in the water ... then they took their love fest overboard.

The lovebirds tooled around in a sea scooter, pausing only to float and make out next to a rock formation.

Back onboard the boat, Oliver made sure to shower off Reese ... getting up close and personal as he rinsed off her butt.

The PDA continued as they went up to the top deck ... Reese sat on Oliver's lap, turned and kissed him as he held her tight.