[R] Maximum # of predictors?

[Jim BRINDLE]

Hello,

Is there anyway one can have more than 11 independent variables in a 
regression model?  To hopefully illustrate: with 13 predictors in my model, 
the last 2 coefficient estimates are "NA".  When I view the summary, it 
indicates that 2 coefficients are "not defined because of singularities".  I 
am using the command:

mod <- lm(y ~ ., data = volumes[,3:22])

I am fairly new to R so I don't know if my issue is something inherent to R 
or my modeling approach.

Any insight would be most appreciated... Thanks in advance