Abstract. A large scale survey of the Galactic center region in the C18 O(J = 1 → 0) transition is presented. This survey was obtained with the 1.2 m Southern Millimeter-Wave Telescope (SMWT) at the Cerro Tololo Interamerican Observatory (CTIO) near La Serena, Chile. It covers the region −1.• 05 ≤ l ≤ +3.• 6 and −0.• 9 ≤ b ≤ +0.• 75 with a grid spacing of 9 , i.e. the sampling is at full FWHP beamwidth. 357 positions were in total observed. After reviewing the instrumentation of the 1.2 m SMWT, the observing techniques, and the methods used in the data reduction, the data of the survey are presented and morphologically described. In addition, data of the HNCO(5 0,5 − 4 0,4 ) line are presented, which was also included in the large bandwidth of the spectrometer.12 CO(1 − 0) measurements performed for comparison purposes are presented and compared with other 12 CO results. The maps of the C 18 O(1 − 0) survey demonstrate that there are great differences between the distribution of the optically thin C 18 O(1 − 0) emission and the usually optically thick 12 CO(1 − 0) emission.

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