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AIMS: We present a sample of candidate quasars selected using theKX-technique. The data cover 0.68 deg^2 of the X-ray Multi-Mirror (XMM)Large-Scale Structure (LSS) survey area where overlapping multi-wavelengthimaging data permits an investigation of the physical nature of selectedsources. METHODS: The KX method identifies quasars on the basis of theiroptical (R and z') to near-infrared (Ks) photometry and point-like morphology.We combine these data with optical (u*,g'r',i',z') and mid-infrared (3.6-24micron) wavebands to reconstruct the spectral energy distributions (SEDs) ofcandidate quasars. RESULTS: Of 93 sources selected as candidate quasars by theKX method, 25 are classified as quasars by the subsequent SED analysis.Spectroscopic observations are available for 12/25 of these sources and confirmthe quasar hypothesis in each case. Even more, 90% of the SED-classifiedquasars show X-ray emission, a property not shared by any of the falsecandidates in the KX-selected sample. Applying a photometric redshift analysisto the sources without spectroscopy indicates that the 25 sources classified asquasars occupy the interval 0.7 < z < 2.5. The remaining 68/93 sources areclassified as stars and unresolved galaxies.

A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique