Facebook has been one of the world's biggest tech firms and a behemoth in social media. However, Mark Zuckerberg’s famed website hasn't seen a surge in viewership, as a new study found its grasp near the top of the most visited websites in the world has slipped a bit, according to CNBC.

The study was conducted by SimilarWeb, an online market research company who supplied CNBC with its data. For years, Facebook and YouTube have battled it out for the number two spot on the list of the five most visited websites in the United States. Facebook has generally won that battle, according to SimilarWeb, but YouTube has already begun to overtake it worldwide.

SimilarWeb offers free reports on websites, even allowing users to compare the metrics for two websites over the past six months. In that time period, YouTube has accrued 24.55 billion total visits compared to Facebook’s 23.15 billion. Between May and July, YouTube was the second most visited website in the world, slightly increasing its margin of victory with each passing month.

GettyImages-157547099 YouTube is gaining on Facebook in monthly U.S. visits. A picture shows a You Tube logo on December 4, 2012 during LeWeb Paris 2012 in Saint-Denis near Paris. Photo: Eric Piermont/AFP/Getty Images

YouTube was still in third place in just the United States, but the gap is closing. SimilarWeb’s more detailed study found that Facebook’s web traffic was cut nearly in half over the past two years. In that timespan, Facebook went from 8.5 billion monthly visits to just 4.7 billion. That does not count traffic in Facebook’s mobile apps, but even with that factored in, it is probably still a loss for Facebook.

The top spot, naturally, belonged to Google. It had nearly 20 billion more total visits over the past six months than either Facebook or YouTube. Google remains the most popular web destination for users who want to find basically anything online, check the news or browse images.

Of course, assuming YouTube becomes the second most popular site in the U.S., the top two spots will both technically belong to Google. The search engine purchased YouTube for a relatively small sum of $1.65 billion in 2006 before both Google and YouTube were reclassified as subsidiaries of the parent company Alphabet.

Alphabet does not generally report specifics on YouTube’s revenue. In late 2016, analyst Mark Mahaney of RBC Capital estimated YouTube had an annual revenue of $10 billion and would continue growing. For more than a decade, YouTube has been the primary place for users to find videos online. It surpassed Facebook as a favorite social network for teenagers earlier this year.