CANTON, Mass. -- Research consulting firm Brand Keys ranked Dunkin' Donuts as No. 1 in the coffee category of its annual Customer Loyalty Engagement Index. This marks the sixth year in a row that the doughnut and coffee chain has topped the list.

For 16 years, Brand Keys has recognized companies that receive the highest loyalty and engagement assessments, surpassing competitors by "delighting" customers, according to the announcement. Customer preferences in the coffee category were based on consistently meeting customer expectations for taste, quality, service and brand value.

"We are truly honored to have earned Brand Keys' top ranking for coffee customer loyalty for six years running. This recognition speaks both to the renowned quality of our Dunkin' Donuts coffee and to the incredible dedication of our franchisees who work to provide our guests with an outstanding experience every day of the year," said John Costello, chief global marketing and innovation officer at Dunkin' Brands. "Through their efforts, our guests have developed a connection with the Dunkin' Donuts brand that is truly unique. We remain committed to keeping America running with our great coffee, baked goods and snacks served in a friendly environment at a great value."

Dunkin' Donuts serves more hot traditional and iced coffee in the United States than any other company, totaling more than one billion cups annually, according to data from The NPD Group’s/CREST service.

"The search for delight by the consumer comes down to a simple equation: understanding customer expectations [and] their desire for brand value, and packaging the two via the brand and product experience offered to customers," said Robert Passikoff, founder and president of Brand Keys. "It's that last part that's difficult, and Dunkin' has continued to manage the brand, and the experience to meet customer desires -- six years in a row. That the customer is delighted with the brand shows up in both the Brand Keys loyalty metrics and Dunkin's bottom line."