The is a rapid train service in Japan operated by West Japan Railway Company (JR West) and Shikoku Railway Company (JR Shikoku) since April 1988. The Marine Liner links Okayama, the capital city of Okayama Prefecture and a major station on the Sanyà  Shinkansen, with Takamatsu, the capital city of Kagawa Prefecture on the island of Shikoku, via the Great Seto Bridge. Operating at a top speed of , the journey takes approximately 55 minutes.
Since 1 October 2003, the Marine Liner has been operated by JR West 223-5000 series EMU trainsets. The car at the Takamatsu end of all trains (except some early morning/late night trains) is a JR Shikoku 5000 series bi-level (double-deck) cab car with reserved seating. Previously, 213 series EMUs were used.
From Okayama to Takamatsu, all Marine Liner trains stop at , and . Most trains also stop at either or , or both. Some early morning and late evening trains make additional stops at intermittent stations on the Seto-Ohashi and Yosan lines.
Unlike the other express trains between Okayama and Shikoku which are Limited Express services (Shiokaze to Matsuyama and Nanpu to KÃ Âchi), the Marine Liner is classified as a service with only a standard fare required. Passengers may upgrade to reserved seating in the bi-level (double-deck) car, in both standard seats (lower deck) or Green Car seats (upper deck and 4 observation seats behind the driver's cab) for an additional fee.
A crew change for the train driver and conductor occurs at Kojima, the boundary station between the two operating railways.
The Marine Liner runs over two sections known collectively as the Seto-Ohashi Line. The Okayama-Kojima section is operated by JR West<sup>1</sup>, and the Kojima-Takamatsu section is operated by JR Shikoku<sup>2</sup>.
<sup>1</sup>Portions run over the JR Uno Line<br> <sup>2</sup>Portions run over the JR Yosan Line
Services are formed as 2-, 3-, 5-, or 7-car formations as shown below with car 1 at the Takamatsu end. All cars are no smoking. Most of the trains use 5-car formations.
The Marine Liner service was introduced in April 1988, using 3-car 213 series EMUs formed as three-car, six-car, or nine-car formations.