Measurements of oceanic isoprene were performed during the OASIS (Organic very short lived substances and their Air– Sea exchange from the Indian Ocean to the Stratosphere) cruises in the Indian Ocean. The OASIS cruises took place in July/August 2014 on board the R/V Sonne I from Durban, South Africa, via Port Louis, Mauritius, to Malé, Maldives. Up to seven samples (50mL) from 5 to 150m depth for each depth profile were taken bubble-free from a 24L Niskin bottle rosette equipped with a CTD. The water samples were, if necessary, stored in the fridge and analyzed on board, within 1 h of collection.