This paper emphasizes the role of primary sources of energy, primarily oil and gas in the future (so-called “energy mix”) with the expected trends in the future. The changes expected by the oil and gas sector in the 21st century have been underlined due to energy decarbonisation. There are intense discussions about the oil and gas future due to the effects of climate change and the announcement that oil is in the final phase of exploitation due to the high depletion of fields around the world. How are the big oil companies responding to these challenges and what are the trends of global energy consumption? In the 21st century, it is necessary to take in account all types of energy with the growth of renewable sources. In the meantime, natural gas is imposed as a bridge between fossil and decarbonised energy, and the trends in the gas segment in the world and in the Republic of Croatia will be emphasized as well. In addition, the new Croatian energy strategy must be aligned with changes in the oil and gas sector, as well as exploration and production of hydrocarbons. Carbon-free energy is still a long way, but the low-carbon energy period has begun.