There was modest growth in oil and gas reserves globally, though the majority came from the United States in 2014, a global oil and gas review found.

Italian energy company Eni said its annual review that oil and gas reserves in 2014 recorded "slight" growth, though most of the gains came from shale basins in the United States.

"The United States surpassed Saudi Arabia and Russia and became the first oil producer in the world, with record growth -- 15.4 percent -- due to tight oil," its review said.

A full-year 2014 profile from the U.S. Energy Information Administration found total U.S. proved oil reserves of 39.9 billion barrels marked a 9 percent increase from the previous year. Total reserves for that year where their highest since 1972. Proved reserves last year increased for the sixth year in a row.

For the first time ever, the United States is in the top 10 in terms of oil reserves, Eni said.

While overall output from the Organization of Petroleum Exporting Countries remains robust, Eni said the "most significant" increase came from non-OPEC members, where gains increased by 2.2 percent.

Iraqi oil production, despite ongoing concerns about terrorism, increased 8.1 percent and Iran returned to growth, boasting a 4.7 percent gain. Libya, meanwhile, "plummeted" to levels during the civil war, when output was around zero.

On the demand side, Eni said there were signs of deceleration. European countries saw demand drop by 1.4 percent, while the United States showed only a 0.4 percent gain. China led the gains for demand, though gains of 3 percent last year where about half of what was recorded during the previous decade.

Low demand and increased production are in part contributing to the steady decline in crude oil prices, which are about 45 percent than they were on this date in 2014.