Add These 20 Fast-Growing Skills to Your Freelancing RepertoireNearly two-thirds of the most sought-after skills are tech related.

Today, more than 35 percent of the U.S. workforce arefreelancers-- and this proportion is growing every year. This means competition is fiercer than ever. In order to be successful and stand out from the crowd, it's vital to develop the most sought-after skills in the U.S. freelance job market.

Related:The Rise of the 6-Figure Freelancer

Freelancing websiteUpworkrecently released itsSkills Index, a list of the 20 freelanceskillsthat grew the most quickly at the end of 2016. From data science to engineering to IT and development, 65 percent of the skills on the list are tech skills, while marketing skills account for 30 percent.

Between 2015 and 2016, demand for each of the skills on the list grew by at least 100 percent. The top 10 saw 200 percent year-over-year growth.

Here are the top five fastest-growing skills:

1. Natural language processing -- a field of computer science that studies human-computer interaction

2. Swift-- a programming language for macOS, iOS, watchOS and tvOS

3. Tableau-- business intelligence and analytics software

4. Amazon Marketplace Web Services-- a web service that supports and helps individuals and companies sell through Amazon.com

5. Stripe-- online payment technology

Between the third and fourth quarters of 2016, data science was the fastest-growing category. With the rise of AI, and as products such as Amazon Echo and Google Home pick up in popularity, it's no wonder natural language processing is the most coveted skill.

Related:4 Ways to Hire and Keep the Best Freelancers

Apple products continue to demand more developers -- in fact, sales of the Apple Watch reached arecord highduring the 2016 holiday season. The programming language behind these devices is Swift, which takes second place on the list of top skills.

If you're a freelancer, check out Upwork's infographic below to find out which skills you should start learning today.