['au..(r)z] = /ˈaʊərz/
['a:(r)z] = /ˈɑːʳz/
In a sentence like “Their car is bigger than ours” ours means our car. “Their car is similar to our car” is grammatically correct, but using ours improves the style.Their methods are worse than our methods.
Their methods are worse than ours.Their books are less interesting than our books.
Their books are less interesting than ours.