(This August 18 story is corrected after NuTonomy says unclear whether will partner with Grab for Singapore commercial service)

SAN FRANCISCO (Reuters) - U.S. self-driving car startup NuTonomy hopes to launch a paid, commercial ride service in Singapore as soon as the second quarter of next year, NuTonomy Chief Executive Karl Iagnemma said on Friday.

Ride services companies are expected to be one of the most important markets for self-driving cars, especially in early years of adoption, when the cost of the technology will likely rule out mass adoption.

Several companies including Alphabet Inc's Waymo and Uber Technologies Inc [UBER.UL] are testing self-driving cars at various locations around the world.

NuTonomy, which currently has a test service in Singapore with southeast Asian ride services partner Grab, plans to charge riders for the new commercial service in Singapore, albeit still with a human driver ready to take over if needed, as is done today in most tests.

Software firm NuTonomy, which works with several car companies including Renault SA, had said it planned to launch commercial service next year, without being more specific on timing. Iagnemma in an interview said he hoped paid self-driving rides would start in the second quarter, although it could be the third or fourth.

NuTonomy also plans to launch a test service with U.S. ride service firm Lyft in Boston later this year.

(Reporting by Peter Henderson; Editing by James Dalgleish)