Levelling observations conducted during the Great Trigonometrical Survey of India (1858--1909) and subsequent observations showed that mean sea level along the coast of India is higher in the Bay of Bengal than in the Arabian Sea, the difference in sea level between Vishakhapatnam and Mumbai (Bombay) being about 30 cm. Using simulations with a 1 1/2-layer reduced-gravity model, we attribute this to the mean, large-scale wind-forced circulation (~60%) and the alongshore gradient in salinity (~40%). The former (latter) is a consequence of the distribution of wind stress (rainfall) because of the monsoon. ¿ 2001 American Geophysical Union