Online bidders have gone into a frenzy after a bottle of rare McDonald's Szechuan sauce went for auction, with the sauce eventually selling for for over $19,000 on eBay. 

The sauce grew in popularity after it was mentioned in the third series of adult sci-fi cartoon Rick and Morty. It was added to the fast food chain's menu in 1988 for a limited time to promote Disney's film Mulan. 

McDonald's handed out a limited number of bottles of the iconic sauce and writer Robert Workman received a bottle and put it on eBay. The sale attracted a lot of attention and eventually sold for US$15,350 (AU$19,443). 

"It's being sold here to settle some bills and help out a couple of charities in the process," he said. 

"The auction includes a NEW, SEALED 64 oz. bottle of the special sauce (which isn't being made right now, so it's VERY rare), along with a special Rick and Morty inspired Pelican camera case, which houses the sauce."

Part of the proceeds were to go to children's charity Extra Life and gaming charity AbleGamers. 

However, Robert has explained that he's had "no response from the buyer yet" since the auction concluded.

“He did not want the sauce, he did not contact me in any way ... we have not heard back and there’s a possibility we may not hear back."

“He’s sitting on a bunch of eBay fees and it’s kind of disappointing. We’re left hanging.”

Robert explained that he thought the bottle would sell for over US$20,000 but "the sauce is still here".