Late in 1964, the Retail Services became part of INA and in 1966 so did Lendava Refinery. The process continued and INA eventually grew to include Zagreb Oil Refinery, Kutina Fertilizer Plant, Petronafta Solin, the Opatovac – Bosanski Brod oil pipeline, Zagreb Inženjering, OKI Zagreb and DINA Omišalj Petrochemical Plants.
From the initial 2.2 million tonnes of refining capacity, in 1979, the capacity of INA Refineries increased to 15 million tonnes, owing to the inauguration of the Urinj plant pertaining to the Rijeka Oil Refinery in 1965, increasing the capacity of Sisak Refinery and construction of the Zagreb Refinery plant at Žitnjak in 1971.
In 1980, Naftaplin recovered three million tonnes of black gold from oil wells. In 1966, INA had 195 petrol stations. In the following ten years their number grew to over 500. In 1979, an oil pipeline was put into operation connecting Omišalj and Sisak and other consumers in the continental part of the country (Bosanski Brod, Pančevo, Novi Sad). INA was one of the main investors in its construction.
From 1980 until 1990 INA was the biggest company in SFRJ. It was employer to 32.000 workers and in 1990 its total revenue amounted 10% of overall Croatian economy. The biggest oil equivalent production in INA's history was in 1988 and amounted 5.1 million tons: 3.04 million tons of oil and 2.1 billion cubic meters of gas.
When Homeland War started, INA very soon adjusted to new working conditions, crisis units were established and many employees participated in defense of the country. Regular production didn't stop, neither did development projects. Restructuring continued, as well as cooperation with foreign partners.
Besides business concept changes, ownership structure also changed. From 1990 INA is state owned company, and from 1993 public limited company. First privatization phase, in which MOL became INA's strategic partner by buying 25 percent plus one share, ended in 2003 and from 2006 INA's shares are published at Zagreb Stock Exchange.
INA in 2000s continues intense exploration and production activities in Croatia and abroad and investments in business modernization. From 2008 until 2014 HRK 16.5 billion was invested in all three main lines of INA’s business (more than HRK 10 billion in exploration and production and more than HRK 5 billion in refineries system development).
Nowadays INA is a medium-sized European oil company with the leading role in oil business in Croatia and a significant role in oil and gas exploration and production, refining and oil and petroleum products distribution in region. It manages two refineries, in Rijeka and Sisak, and has a network of 439 retail stations. INA has a clear vision of the future and its role, proudly continuing half a century long tradition.