The wording wasn't clear, but the example code given was: Using an interpolated double-quoted string is faster than using 2 or more concatenated single-quoted s

The wording wasn't clear, but the example code given was: Using an interpolated double-quoted string is faster than using 2 or more concatenated single-quoted strings. That doesn't no longer holds true when comparing a non-interpolated double-quoted string and the identical single-quoted string Tho as others have said, if you're interested enough in optimization to worry about what type of quote you're using, you should just use opcode caching (APC) which will optimizing string parsing along with everything else.