Boys called Oliver are going to utterly dominate NSW primary school roll-calls in coming years – if they aren't already.

The name topped the state's Register of Births, Deaths and Marriages list of 100 most popular baby names (for boys) for the fourth year in a row last year.

The second most popular boys' name, William, has sat in second place for each of those four years, having been toppled from the number one spot it held in 2013.

For girls, Charlotte bumped out the 2016 winner – Olivia – for first place in 2017. The two girls' names have been neck-and-neck for first and second place for the past three years.