In agile methodologies communication between programmers is very important. Some of them (e.g. XP or Crystal Clear) recommend pair programming. There are two styles of pair programming: XP-like and side-by-side (the latter comes from Crystal Clear). In the paper an experiment is described that aimed at comparison of those two styles. The subjects were 25 students of Computer Science of 4th and 5th year of study. They worked for 6 days at the university (in a controlled environment) programming web-based applications with Java, Eclipse, MySQL, and Tomcat. The results obtained indicate that side-by-side programming is a very interesting alternative to XP-like pair programming mainly due to less effort overhead (in the experiment the effort overhead for side-by-side programming was as small as 20%, while for XP it was about 50%).