His main research has been in the application of physical sciences to archaeology and the environmental sciences and in particular in the use of radiocarbon isotope studies:
Radiocarbon dating in Archaeology
As director of the Oxford Radiocarbon Accelerator Unit, he has been involved in many different archaeological projects. These projects include those that are led from Oxford, and those that are collaborative with scholars elsewhere. His primary focus in recent years has been in the archaeology of the eastern Mediterranean (Aegean, Egypt and the Levant), and in the Paleolithic period (with Tom Higham).
Quaternary chronology and Environmental Science
Radiocarbon dating (0-50ka) provides one of the main ways for dating the later Quaternary (0-2.5Ma) and in particular the dating of modern human expansion into Europe, Neanderthal extinction and faunal/human responses to the climate variability during the last glacial cycle. Much of his current research is directed to improving radiocarbon as a method for quaternary research. He is a member of the international INTCAL committee that oversees the calibration of radiocarbon. Two current research grants are directed at improving the global datasets for radiocarbon calibration.
The use of numerical modeling methods in chronology
Over the last 15 years he has worked extensively on the application of Bayesian statistical methods to the study of chronology in both Archaeology and Quaternary environmental research. He has formulated a systematic approach to approaching chronological research, which is embedded in the widely used software package OxCal.
Development of Nuclear Instruments and Methods
Trained as a physicist, much of his early-career research was in the development of Accelerator Mass Spectrometry (AMS) techniques including the development of gas ion sources for AMS which allows the measurement of very small samples and a technique, GC-AMS with applications in the environmental and biological sciences. More recently he has been most concerned with the development of high-precision techniques and their applications to archaeological and environmental problems.