Olsen, 27, and her 44-year-old beau have been spotted checking out prices on marital jewellery here, which has sparked speculation they are about to get engaged.
"Mary-Kate has been seen several times in the last three weeks checking out huge engagement rings at the Neil Lane store," a source told nypost.com.
"She really likes cushion-cut diamonds, and all of the rings she has looked at are over five carats. She has narrowed it down, but still has not made a final decision," added the source.
In 2012, Sarkozy split from his wife of 13 years, Charlotte Bernand, and they have two children together.
Olsen previously dated artist Nate Lowman for over two years before splitting in 2010, while Sarkozy romanced actress Stella Schnabel for a year before their break-up last March.
--IANS (Posted on 10-12-2013)