The world's top 12 publicly-traded oil producing companies saw their total net income and revenues decline in the first quarter of 2019, according to the data on these firms' financial results.

American ExxonMobil, Chevron, ConocoPhillips, Halliburton, Schlumberger, Baker Hughes, British BP, Royal Dutch Shell, French Total S.A., Italy's Eni, Russia's Rosneft and Norway's Equinor saw their collective revenue and net income decline year-over-year.

These 12 companies saw their total revenue fall by 4.63% to around $393.5 billion in the first quarter of 2019, from approximately $412.6 billion in the first quarter of 2018, according to the data.

The oil giants also had their collective net income decline to $23.6 billion in the first three months of this year – a 4.45% decrease from $24.7 billion from the same period a year ago.

Royal Dutch Shell led the 12 oil and gas giants to post the highest net income and revenue in the January-March period of 2019.

The company had a net income of $6 billion in the first quarter of this year, followed by Total S.A. with earnings of $3.11 billion, and Chevron with an income of $2.65 billion.

Shell saw revenue of $85.66 billion in the first three months of 2019. During that period, BP ranked second with $67.41 billion, while ExxonMobil followed in third place with $63.62 billion.

Oil prices fall by around 5%

The majority of the decrease in collective net income and revenue for the oil giants was due to a fall in crude oil prices, which saw a decline of around 5% year-over-year.

International benchmark Brent crude averaged $66.80 per barrel in the first quarter of 2018, but lost 5.54% to average $63.10 a barrel in the January-March period of 2019, according to the U.S. Energy Information Administration (EIA) data.

One of the major reasons behind the decline in the Brent crude price was because global oil production showed a year-over-year increase to contribute to the glut of supply in the global oil market.

Global oil production reached 94.42 million barrels per day in the first quarter of this year, an increase of 3.2% from the same period a year ago, according to OPEC's Monthly Oil Market report for April 2019. Oil supply worldwide totaled 91.52 million barrels per day in the first quarter of 2018.

The year-over-year increase in global oil supply came from non-OPEC countries in the January-March period of this year. Non-OPEC oil producing nations saw their total output rise by 7.7% to 63.97 million barrels per day in the first quarter of 2019 compared to 59.39 million barrels per day in the first quarter of 2018.

OPEC nations, on the other hand, saw their collective production decline to 30.45 million barrels per day in the first three months of this year, from 32.13 million barrels per day over the same period of last year, to post a 5.2% decline in output, according to OPEC's April report.