How can I declare a thousand separator in read.csv?

since there is an "r" tag under the question, I assume this is an R question. In R, you do not need to do anything to handle the quoted commas:

> read.csv('t.csv', header=F)
     V1          V2          V3          V4
1 Sudan  15,276,000  14,098,000  13,509,000
2  Chad      209000      196000      190000

# if you want to convert them to numbers:
> df <- read.csv('t.csv', header=F, stringsAsFactor=F)
> df$V2 <- as.numeric(gsub(',', '', df$V2))

Looking at that set of data you could parse it using ", " (note the extra space) as the seperator intead of ","