Twitter may be more influential than Facebook in helping drive consumers’ shopping decisions, according to Kantar Media Compete’s quarterly Online Shopper Intelligence Study.

The study, based on a survey of 2,574 online shoppers between July 14 and August 8, found that 35% of consumers said Twitter was influential or extremely influential in their decision to buy a product. That compares with 24% who said Facebook helped guide a purchase.

However, the dominant way to reach consumers remains e-mail, the report says. Nearly one in three consumers receives more than 20 e-mails from retailers in a week. And 89% percent of all respondents at least occasionally click through from an e-mail to a retail web site or they visit a retail site soon after reading the message.

While social media and e-mail marketing are relatively well-established, short messaging service (SMS) texts offer retailers an untapped channel for brands to reach shoppers, says the report. That’s because during a typical week 72% of shoppers don’t receive a single text message from retailers.

SMS texts can be valuable because promotional offers are driving purchases. One in five respondents said they used a coupon code for their last purchase—and 60% of those shoppers said they wouldn’t have bought that item had they not obtained the code.