A Web-based computer simulation of an actual laboratory experiment was developed for the MIT Laboratory classes. This virtual experiment, which we call the Web Lab, was introduced into the "Chemical Engineering Projects Laboratory" in spring 1999 and the “Chemical Engineering Process Laboratory" in fall 1999. Among the goals of these courses are to teach students laboratory, data analysis, and communication skills, including writing individual and collaborative team technical reports, making oral technical presentations, and collaborating in the laboratory in teams of three. The aim of this Web Lab was to provide a common experience early in the term in which students collect and analyze data and prepare a formal technical report with tables and figures. One feature of the virtual experiment was that students controlled the experiment and made actual readings from two graduated scales displayed on the monitor. The data collected reflected experimental errors associated with these readings as well as systematic and random errors built into the simulation software. The motive for using a Web-based environment was the notion that it would provide a means for rapidly and easily collecting data for analysis along with the convenience of running the experiment at any time and with any operating system. During its initial use in the Projects Laboratory course (enrollment of 54 juniors and seniors), the Web Lab was evaluated as a learning tool, and the following conclusions emerged: