Cementing a string in one stage is a challenging task, especially in the presence of weak formations. Cement-slurry losses during placement are highly possible if the equivalent-circulating density (ECD) exceeds 11.0 lbm/gal during placement. A conventional method to overcome this challenge is to use multistage cementing by setting the stage tool above the lost-circulation zone. However, field data indicate that the tool can fail, thus causing serious delay and economic losses. In addition, stage tools are considered weak points and are not good for a long-term seal. A second method for zonal isolation is to use low-density cement (LDC). In this study, we considered cementing the intermediate and production casings in the S-1 (sandstone) and S-2 (carbonate) shallow formations and the BJD (dolomite) deep formation in a single stage using lowerdensity cement based on hollow microspheres, at 9.4 lbm/gal. The shallow conditions simulated in the laboratory tests were 150°F curing temperature, 2,400-psi conditioning pressure, and 1,800-psi confining pressure for 3 months. The deep conditions were 260°F curing temperature, 5,000-psi conditioning pressure, and 3,000-psi confining pressure, also for 3 months.Hollow-microspheres cement was used in oil and gas wells without encountering any operational problems. However, the high cost of microspheres cement was a limitation for potential field application. In this study, we present extensive laboratory work to optimize hollow-microspheres LDC by the elimination of microfine cement from the blend. Experimental studies (shrinkage, compressive strength, porosity, gas and brine permeability, and chemical analysis of cement) were conducted to determine the effect of this optimization on the properties of cement.Data generated during the 3 months supported the use of the optimized system to cement casings at the shallow conditions tested. The removal of microfine cement did not reduce the compressive strength, with an average of 2,013 psi; no shrinkage was observed, and no increase in permeability was noted during the three months of testing. The use of the optimized system did help in bringing cement to the surface in one stage. The cost of the optimized blend was 40% less than conventional hollow-microspheres LDC.This paper presents case histories that include job design, job execution, and evaluation of the LDC. Field treatments were successful and maintained isolation for more than 3 years.