In this study, the stability conditions and the modes of oscillation in a four parallel-channel upflow boiling system with cross-connections have been experimentally investigated using Freon-11 as the test fluid. Two major modes of oscillation, namely density-wave and pressure-drop type oscillations, have been observed. When two modes of oscillation occurred simultaneously some temperature oscillations were observed in most instances. Transient instabilities resulting from a step increase in power input and a step decrease in flow rate have also been investigated. The results have been compared with other boiling flow systems.