Mars - the packaged food conglomerate that owns Snickers, Cheez-It and other snack brands - will soon add Pop-Tarts, Eggo Waffles, Pringles and more to its portfolio.

What Happened: The McLean, Virginia-based company is set to acquire Kellanova (K  ) for $36 billion, or $83.50 a share.

Kellanova brought in around $13 billion in revenue last year, while Mars' annual revenue was around $45 billion. The two companies were reportedly working out the details earlier this month after Kellanova reported strong second-quarter results.

The transaction, should it finalize in 2025, would help Mars leapfrog Publix to become the third-largest American private company behind Koch Industries. Until then, the top-five ranking of the largest U.S. privately held companies is as follows:

Cargill, Incorporated: The Minnesota-based agricultural and food company specializes in oils for processed foods. Cargill does more than $175 billion in revenue annually, according to Forbes.

Koch Industries is a multi-sector conglomerate that operates in the oil, petroleum, gas and fertilizer industries. Koch does around $125 billion in revenue and spends billions annually on political contributions and lobbying.

Publix Supermarkets, headquartered in Florida, does around $55 billion in revenue and is one of the largest grocery chains in Florida. Publix also has locations in other southern states such as Georgia and Tennessee.

Mars is known for making confectionery items, including Mars bars, Twix, Milky Way and Three Musketeers. It also produces non-confectionery snacks (i.e., Combos, Ben's Original and Dolmio pasta sauce) and an array of pet foods.

H-E-B Grocery Company is fifth on the list, raking in around $44 billion in revenue annually. Like Publix, H-E-B has carved out a significant market in the southern U.S., with most of its locations in Texas.

Other notable American private companies that did not break the top five include Lego (around $10 billion in revenue), Chick-fil-A (around $12 billion in revenue) and Staples (around $8 billion in revenue).