Event messages are received from a first source, each has a subscription based-sequence number and a time stamp. The order of events within the first event source are determined on the basis of the subscription based-sequence number. Additional event messages are received from a second source each having a subscription based-sequence number and a time stamp. The events from the second event source are ordered with respect to the first event source on the basis of the time stamp within each of the at least two event messages from the first event source and the another at least two event messages from the second event source.