NEW YORK (The Deal) -- With a pack of deals for makers of products for humans' furry friends, e-commerce players are also hitting the auction block.

Two of those companies up for sale are Foster and Smith, which does business as Drs. Foster & Smith and Tabcom, formerly Pets United LLC, , according to people familiar with the situation.

It's expected that both strategics and private equity firms will be interested buyers because of consumers' willingness to spend more on their pets.

Listed PetMed Express (PETS - Get Report) , the Pompano Beach, Fla.-based pet pharmacy retailer doing business as 1-800-PetMeds, at one point also considered a sale, according to sources familiar with the company, but is no longer formally on the market. PetMed Express has a market cap of close to $270 million, and revenue of about $230 million.

Drs. Foster & Smith declined to comment, while Tabcom and PetMed Express did not immediately respond to requests for comment.

Drs. Foster & Smith, the Rhinelander, Wis.-based hybrid catalogue and e-commerce business that sells a wide variety of pet products, is one of the larger players in the sector.

The company has annual revenue of $250 million, according to a source, and is profitable. About half of Drs. Foster & Smith's business is generated online. It is a purveyor of pet food and treats, pet bedding, cages and crates, toys and grooming products. It was founded in 1983 by veterinarians Dr. Rory Foster, Dr. Race Foster and Dr. Marty Smith.

TABcom, based in Hazleton, Pa., was founded in 2002 by brothers Alex and Carlo Tabibi, and owns a number of websites and businesses, including 1800Petsupplies.com, Horse.com, Dog.com, Statelinetack.com, Garden.com, Ferret.com, Bird.com, Fish.com, PetFood.com, Bike.com, Ecopets.com, Greenhouse.com and Saddle.com.

In 2007, according to Inc. magazine, it was one of the fastest growing companies in the U.S. with revenue of more than $60 million. Today, the company has about $85 million in revenue and is run by Glen Demeraski, its chief executive, who joined TABcom in 2009.

The online pet retailers join PetFlow, which has retained investment bank Lazard as its financial adviser in a sale of that business. New York-based PetFlow could either be acquired by another e-commerce player hoping to consolidate or by one of the legacy brick-and-mortar players such as PetSmart (PETM) or Petco Animal Supplies, a source said.

PetFlow and Lazard have not responded to requests for comment.

PetFlow generated $39 million in revenue in 2013 and expects to hit the $50 million revenue mark. The company has grown rapidly since it was founded by Alex Zhardanovsky and Joe Speiser in 2010.

By November of that year, it was doing $250,000 in revenue per month, and by May 2011, it was churning out $1 million in sales per month, according to CNN Money. By early 2012, PetFlow was closing in on producing $2 million in revenue a month, and was on track to generate more than $20 million in sales that year, according to prior reports from The Deal.

In 2011, PetFlow raised a Series B round of $10 million led by venture capital firm Lightspeed Venture Partners. Prior to that, PetFlow had raised $5 million from investors.

More recent deals in the space include Chewy.com, which took outside capital and has revenue of more than $200 million, according to a source. That company is not currently for sale.

PetSmart on Aug. 19 announced it had acquired Pet360 Inc., a pureplay e-commerce player, for $130 million.

The pet sector has been active, but not so much on the retail side of the equation, aside from pressure applied by activist hedge fund Jana Partners LLC on PetSmart to explore a sale to private equity.

Most of the deals, not to mention initial public offerings, have been focused on the makers of pet products. Freshpet Inc., the Secaucus, N.J.-based maker of refrigerated fresh pet food, has filed for a $100 million IPO this year. Blue Buffalo Co. Ltd. is also likely headed for a public listing late this year. The Wilton, Conn.-based natural pet food business is said to have in the vicinity of $750 million in revenue, 20% Ebitda margins, and could achieve a $3 billion valuation, said one source.

In April, Mars Inc. bought Procter & Gamble's (PG - Get Report) pet food brands Iams, Eukanuba and Natural for $2.9 billion.

In May 2013, Big Heart Pet Brands Inc., then known as Del Monte Foods Co., acquired Natural Balance Pet Foods Inc., a competitor to Blue Buffalo with $300 million in sales. That purchase from private equity firm VMG Partners was for $500 million, a source said.