Hi, My problem does not happen all the time, nor with all files I save to csv format. I can send my test file (format rda or csv) to whoever would like to replicate (and hopefully explain) my problem. In short, I have a dataset with mostly numerical variables. One of my variable is called pfi2 and is definitely numerical, as shown by this: > summary(test$pfi2) Min. 1st Qu. Median Mean 3rd Qu. Max. 0.00000 0.00000 0.00000 0.01208 0.01500 0.08900 Yet, when I export to a text file and asking for comma as the decimal separator, I get a period as the separator for this variable, whereas all the other variables have the desired comma as separator. write.table(test, "out1.csv", sep = ";", dec = ",", row.names = F, col.names = TRUE) write.csv2(test, "out2.csv") First 5 lines of out1.csv: "trait";"tfi";"sto_wt";"pfi2";"pfi_st";"focc";"sed";"mob";"date";"latitu de";"longitud";"hre_deb";"temp_fon";"strate";"lat.km";"long.km";"temp_.2 5C" 10;0,764;5,1;0.007;0,213;0,143;0,048;0,095;"05/08/99"; 47,49;-58,9267;"20:11";4,9;302;-167,791200000000;230,761439786593;4,88 106;0,566;3,3;0.089;4,762;0,25;0;0,25;"14/08/99"; 49,84;-59,655;"23:25";4,4;814;93,3408000000004;168,052052432345;4,38 110;1,517;8,3;0.003;0,172;0,25;0;0;"15/08/99"; 49,88667;-60,2167;"04:57";0,3;833;98,5267704000003;127,674990442535;0,38 111;1,232;7,5;0.016;1,309;0,25;0;0;"15/08/99";49,84;-60,1617;"06:14"; 0,1;833;93,3408000000004;131,739909589075;0,12 I'm sorry but I wanted to make this lighter by removing more variables from my original dataset, but the problem disappeared, so I had to keep these variables to show you the problem SOMETIMES happen. You'll notice that the 4th variable has periods for decimal markers. The write.csv2 command produced the same problem. With other files I sometimes get commas for all variables, sometimes I get more than one variable with periods. It is frustrating. So let me know if you'd like the data file, Sincerely, Denis Chabot platform powerpc-apple-darwin7.9.0 arch powerpc os darwin7.9.0 system powerpc, darwin7.9.0 status major 2 minor 1.1 year 2005 month 06 day 20 language R