There is scarcity of literature on the application of social media for the marketing of university library products and services in Nigeria. The aim of this study is to ascertain the extent of adoption of social media in university libraries. All eight university libraries in Delta and Edo States of Nigeria were selected. Using survey design, a sample of 77 librarians was selected through census sampling technique. The results showed that face to face, notice boards, bulletins and internal memos are the most used conventional methods of service delivery. The most available virtual methods of service delivery are library websites, Twitters, e-bulletins, telephone calls, WhatsApp and Facebook while blogs, Flickr, YouTube, text messages and E-mails are barely available for use. The major social media available (inclusive of the virtual methods) are My Space, Research Gate, Wikis, Instagram, Slide Share, LinkedIn, SMS and online public catalogues while Orkut, Picassa/Flickr, Pinterest, Delicious, RSS feeds and social bookmarking. Only Facebook, SlideShare, LinkedIn, SMS, WhatsApp are used at a moderate extent while others have either low or no extent of use in the marketing process. Social media helps save time, and ease interaction and sharing of information and incorporate users into decision making processes by the libraries hence its adoption. Social media are used on an average of once/twice monthly for one to three years now. Though, there was clear indication of inefficient utilization of social media tools for marketing in university libraries in Nigeria from the study. It was thus recommended that a campaign is needed for greater awareness and adoption by librarians and library users’ acceptance.