Thanksgiving e-commerce sales increased 29% year over year and Black Friday online sales increased 24%, according to data from e-commerce platform and technology service provider Salesforce Inc. Commerce Cloud.

Mobile commerce was a big contributor to sales growth on both days, says Rob Garf, vice president of industry strategy and insights for Salesforce Commerce Cloud, which bases its data off of 2,750 e-commerce sites, 500 million global shoppers in 53 countries and billions of transactions on its commerce cloud. Salesforce is the e-commerce platform provider for 80 retailers in the Internet Retailer 2017 Top 1000, according to Top500Guide.com.

On Thanksgiving, smartphones generated 61% of  traffic to e-commerce sites on Salesforce’s platform, up from 53% last year, and they accounted for 46% of orders, up from 37% in 2016.

Similarly on Black Friday, which is the Friday after Thanksgiving, smartphones generated 60% traffic for Salesforce’s merchants, up from 52% last year, and 42% of orders, up from 34%. The Salesforce analysis does not include sales transacted within mobile apps.

On Cyber Monday, which is traditionally skews toward desktop devices because shoppers return to work, mobile generated 37% of orders, up from 29% last year, and 56% of visits, up from 48%, Salesforce finds.

E-commerce platform provider Shopify finds that mobile sales outpaced desktop throughout the four-day period from Black Friday through Cyber Monday (Nov. 23-27) and accounted for 64% of sales, which is a 10% year-over-year increase.

On Cyber Monday, for example, mobile commerce accounted for 60% of online sales, an 11% year-over-year increase, according to Shopify, which is the e-commerce platform provider for 22 retailers in the Top 1000. Shopify’s mobile sales data only includes smartphones, not tablets. Its data is based on the 500,000 merchants that use its platform.

Retailers’ push to offer shoppers a smooth mobile shopping experience helped boost mobile sales, Salesforce’s Garf says.

“We’re all used to having our mobile devices tethered to us,” he says. “It’s the remote control of our daily lives.”

Salesforce also finds that retailers offered a higher average discount on Thanksgiving, at 29%, compared with Black Friday, at 28%. Cyber Monday’s average discount rate was 29%.

On Thanksgiving and Black Friday, 85% of orders shipped for free, while 89% shipped free on Cyber Monday.

“In the consumer’s mind, free shipping isn’t a ‘nice’ to have, it’s an expectation,” Garf says.

Salesforce estimates that 35% of the holiday season’s online shopping was completed by the end of Cyber Monday. By Dec. 3, 50% will be complete, it estimates. Garf says this leaves retailers “a lot of runway” left to generate holiday sales.

He suggests retailers continue to offer “personalized experiences,” such as emails tailored to shoppers’ preferences, and that they retarget consumers with ads on social media for relevant products and product recommendations.

Retailers that generate product recommendations with artificial intelligence—meaning the tool factors in data learned over time based on how shoppers interacted with a retailer’s website—saw benefits on Black Friday. Just 6% of consumers tracked by Shopify clicked on a recommended product, yet those clicks accounted for 30% of revenue, Garf says. Salesforce did not share how many of its merchants have product recommendation engine with artificial intelligence.

Another key to improved customer experience is for retailers to ensure their call centers are properly staffed and that consumers can easily connect with them. Merchants can do so by embedding service agents into live chat on their site or making sure they monitor requests or concerns expressed on social media, he says.

“Do it on the consumer’s terms and not on the retailer’s terms,” Garf says, noting that merchants should offer multiple channels where consumers can seek customer service assistance.