The OPEC agreement on higher oil production will mainly benefit to Saudi Arabia which will gain market share on the oil market. The increase in oil production is global and there is no distribution by country. Saudi Arabia can easily increase its production but Iran will not be able to increase it (sanctions) and Venezuela is in a terrible mayhem and its production is trending downward.
In other words, Saudi Arabia and the US are the winners of this agreement.
Read more here
www.bloomberg.com/view/articles/2018-06-22/trump-and-saudis-win-big-in-opec-deal