Precise bulk-density (BD) measurements of organic soils, and mineral soils with high organic content, are difficult to make but critical for accurate estimates of soil-mass properties such as soil-organic carbon (SOC) storage. For a SOC-sequestration study in the Mississippi River Deltaic Plain, 58 cores were collected using 7 methods. Percent core compaction was variable by method. Number of cores, and mean percent compaction, by core method, were 7, 35.5, pushed whole core; 20, 6.6, pushed half core; 11, 6.5, pounded half core; 7, 22.2, vibracore; 6, <1, Hargis sampler; and 7, <1, McCauley sampler. Cores were sampled every 2 cm for BD and SOC analyses. Bulk-density and SOC data from the short push-cores and longer vibracores were used to estimate the SOC storage at locations within fresh, intermediate, and brackish marsh, backswamp, swamp, levee, and distributary environments. Bulk density varied inversely with SOC when SOC was <30 weight percent and showed no relation when SOC was >30 weight percent. Median BD values (g cm^-3) stratified by SOC content (<12, >=12<18, >=18<30, >30) ranged from 0.07-0.56 (fresh marsh, n=16), 0.07-0.41 (intermediate marsh, 5), 0.04-0.23 (brackish marsh, 21), 0.24-1.13 (levee, 6), 0.17-0.53 (distributary, 4), 1.32-1.35 (backswamp, 2), and 0.12 (swamp, 1). Median SOC values for these same groups ranged from 1.05-45.08 weight percent (fresh marsh), 6.33-39.67 (intermediate marsh), 0.47-39.25 (brackish marsh), 0.76-23.61 (levee), 8.55-30.43 (distributary), 0.97-1.09 (backswamp), and 37.81 (swamp). Data from cores collected with the Hargis and McCauley samplers at fresh and intermediate marsh localities were compared with push-core and vibracore data in a balanced ANOVA to test the effects of coring method on the reproducibility of BD measurements. Spatial variability and sampling technique both contributed to observed BD differences between push-core data and data from the other methods. Samples obtained by push-core methods provided the most consistent results.