Abstract: A computer-implemented method and apparatus are provided for monitoring transactions involving a conserved resource, for example to monitor operation of a network of cash dispensing machines. The method comprises receiving into a computer monitoring system a plurality of data feeds relating to the transactions to be monitored, each data feed comprising successive rows of data, each data row in a given data feed comprising multiple data elements in accordance with a predetermined pattern. The method further comprises performing, within the computer monitoring system, a grouping analysis, on the received data feeds. The grouping analysis determines at least one data element in a first data feed from said plurality of data feeds corresponding to provision of said conserved resource, and at least one data element in a second data feed from said plurality of data feeds corresponding to consumption of said conserved resource.