To determine which number is larger between 9.11 and 9.9, we need to compare their decimal places.

Both numbers have the same whole number part, which is 9.

Now, let's compare the decimal parts:
For 9.11, the tenths digit is 1.
For 9.9, the tenths digit is 9.

Since 9 is greater than 1, the number 9.9 is larger than 9.11.

Alternatively, we can "pad" the shorter decimal with a zero to make it have the same number of decimal places as the longer one:
9.11 has two decimal places.
9.9 can be written as 9.90 (meaning 9 and 90 hundredths).

Now compare 9.11 and 9.90:
From left to right:
The units digit is 9 for both.
The tenths digit for 9.11 is 1. The tenths digit for 9.90 is 9.
Since 9 is greater than 1, 9.90 is larger than 9.11.

Therefore, 9.9 is larger.

The final answer is $\boxed{9.9}$.
