Google's digital-ad business remained very profitable during the last quarter, helping its new parent company, Alphabet, become the most valuable U.S. company ahead of Apple. On Monday, Alphabet released its first quarterly earnings report since Google reorganized itself under the new company. Alphabet said consolidated revenue jumped 17.8 percent to $21.33 billion in the fourth quarter ended Dec. 31, from $18.10 billion a year earlier.

Alphabet is running mostly experimental businesses - which include glucose-monitoring contact lenses, Internet balloons, products aimed at eliminating the human driver to curing cancer. Those operations posted an operating loss of $1.2 billion on revenue of $151 million in the fourth quarter.

Google, also part of Alphabet, produced an operating profit of $6.8 billion on revenue of $21.2 billion. Google's advertising revenue increased nearly 17 percent to $19.08 billion, while the number of ads, or paid clicks, rose 31 percent, the company said.

Google's Chief Financial Officer Ruth Porat attributed the strong earnings to "increased use of mobile search by consumers," as well as "ongoing momentum" in YouTube and programmatic advertising.

Alphabet's combined share classes were worth $555 billion, compared with Apple, which had a value of about $534 billion.