Portland-based Oakhurst Dairy will have to pay an estimated $13 million in unpaid overtime after losing a court battle over a missing comma.

A group of delivery drivers in the US state of Maine will be paid an estimated $13 million in overtime after winning a three-year legal dispute with their employer, with an appeals judge ruling in favour of Oxford comma supporters everywhere.

The Oxford comma, also known as the serial comma, is a comma placed immediately before a conjunction such as “and” or “or” in a series of three or more terms, as in: “First, second, and third.”

While generally not used by journalists, the Oxford comma is often used in academic publications. Debate has raged for years about its use — opponents feel the extra comma is unnecessary, but supporters claim it helps resolve ambiguity.

The Chicago Manual of Style, for example, cites the following example: “She took a photograph of her parents, the president, and the vice president.” Without the comma, she is taking a picture of her parents, who are the president and vice president.

In the case of the truck drivers, they argued that the relevant state employment law pertaining to overtime was ambiguous because of a missing comma. The law says that overtime rules do not apply to:

The canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment or distribution of:

(1) Agricultural produce;

(2) Meat and fish products; and

(3) Perishable foods.

Three drivers brought the class-action suit against Portland-based Oakhurst Dairy in 2014, arguing that their industry was not carved out by the exemption. The question was whether the final part of the sentence, “packing for shipment or distribution of”, referred to one profession or two.

“For want of a comma, we have this case,” judge David J. Barron wrote.

“The delivery drivers contend that, in combination, these words refer to the single activity of ‘packing’, whether the ‘packing’ is for ‘shipment’ or for ‘distribution’,” the court wrote in its judgment.

“The drivers further contend that, although they do handle perishable foods, they do not engage in ‘packing’ them. As a result, the drivers argue that, as employees who fall outside Exemption F, the Maine overtime law protects them.”

While a lower court ruled that, despite the missing comma, the law “unambiguously intended for the last term in the exemption’s list of activities to identify an exempt activity in its own right”, the appeals court disagreed. It found that there was enough ambiguity in the reading of the sentence to rule in the drivers’ favour.

“That comma would have sunk our ship,” David Webbert, a lawyer who represented the drivers, told The New York Times on Wednesday.

While only three drivers brought the case, some 75 will share in the estimated $US10 million ($13 million) unpaid overtime. The drivers earned between $US46,800 and $US52,000 ($60,900 and $67,700) a year, and worked an average of 12 extra hours per week for which they should have been paid time-and-a-half.

Webbert denied he was representing Oxford comma supporters everywhere, telling The New York Times he was only representing the truck drivers. “In this situation, it did create an ambiguity, which means you have to either add a comma or rewrite the sentence,” he said.

Oakhurst president John Bennett told the paper on Thursday that “our management team values our employees and we take employee compensation seriously”. “We believe we’re in compliance with state and federal wage laws, and we’ll continue to defend ourselves in this matter,” he said.

Oakhurst employs 200 people and makes around $US110 million ($143 million) in revenue a year, according to its website.