ABSTRACT From Dec/84 until the end of 87, PETROBRÁS have drilled 28 wells in deep waters (deeper than 500m) using dynamic positioning units. This paper presents the drilling program evolution, from the first well up to now, showing the improvement of efficiency and costs control as well as the alternatives selected to overcome the problems faced during the operations. Among the achievements, a special attention is given to a new permanent guide base, designed and developed by PETROBRÁS, which allows to improve the spud in of exploratory wells and the subsea completion. INTRODUCTION At the end of 1984 PETROBRÁS started, with the drill ship Pelerin, operations utilising dynamic positioning (DP) rigs. The first well, 1-RJS-219A, in 853 meters water discovered a giant oil field named Marlim. In 1985, six wells were drilled in water depths between 621 and 942 meters with two DP ships - Pelerin and Ben Ocean Lancer. Due to the excellent results achieved, PETROBRAs managed to operate in 1986 four drill ships, having contracted the PAC NORSE I and the SEDCO 472. During this period, thirteen wells were drilled in water depths varying from 550 to 1250 meters. In 1987, eight wells were spudded in by using the OS SEDCO 472 and the semi-submersible SEDCO 709. In this period, the national record of 1565 meters water was achieved with 1-RJS-367 well, at the Albacora field. This large quantity of wells provided PETROBRÁS the informations necessary to develop new techniques and new equipment which increasingly proved to be indispensable for the effective reduction of the drilling costs and for having these wells onstream in the future. GENERAL CONDITIONS OF OPERATION SITE The exploration efforts were concentrated on the southeastern drilling district in an area located at Campos BaBin, between the latitudes of 22° and 23° south and longitudes of 39,5° and 40,5° East, distant 190km from Macaé where the support base is located. In this strip, large structures were discovered as Marlim, Albacora and South of Marlim (yet to be delimited). In addition to this area, one dry well (1-BAS-80/978m water) was carried out in Jequitinhonha Basin and other two (1-SES-92/1110m water and 1-SES-93/1112m water) in Sergipe/Alagoas Basin, with promising results (FIG. 01). Despite the great depth, the exceptional proximity of the coast (35km) makes this area to become of great interest for future development. The description of the operation site conditions will be restricted to Campos Basin area where 90% of the wells were carried out. Water Depth - In a first stage, the area in focus was situated between 400 and 1000m water, where the impossibility of divers intervention and resulting necessity of special equipment had to be considered. The concentration of wells in these waters resulted in the discovery of fields which showed good prospects of being extended to even more deeper waters. As a consequence, in OCT/86 a second stage initiated with rigs capable to work in waters up to 1800m. Waves and Winds - The oceanometeorological conditions of the area with occurrence above 60% are: winds of 13 to 24 knots in the NE direction and waves of 1,2 to 1,8 meters height, with periods from 7 to 8 seconds.