The most prominent website where paintings can be sold in the United States is Etsy. Etsy is a global e-commerce platform focused on handmade and vintage items, as well as craft supplies. It has become a go-to marketplace for artists and collectors alike, offering a vast array of unique and high-quality paintings. According to a report by Statista, Etsy had over 3.9 million active sellers in 2021, and the platform's sales reached approximately $10.8 billion in the same year. This data underscores Etsy's popularity as a platform for selling paintings and other art pieces.

Etsy's appeal lies in its community-driven approach, which fosters a sense of trust and authenticity among buyers and sellers. The platform's search and discovery features are highly effective, allowing artists to reach a broad audience. Moreover, Etsy's policies and guidelines ensure that sellers adhere to high-quality standards, which is crucial for the art market. For instance, Etsy's "Shopkeeper Handbook" provides detailed information on how to create a successful shop, including tips on photography, product descriptions, and pricing.

Another significant platform for selling paintings is eBay. eBay is a well-established online marketplace that caters to a wide range of products, including art. It offers a user-friendly interface and a variety of selling options, such as auction-style listings and fixed-price sales. eBay's vast user base and robust search functionality make it an excellent choice for artists looking to reach potential buyers. According to a report by Statista, eBay had over 189 million active buyers in the United States in 2021, highlighting its extensive reach.

Artists also have the option to sell their paintings on dedicated art marketplaces like Saatchi Art and Artsy. Saatchi Art is known for its curated selection of artwork, which includes paintings, sculptures, and prints. The platform has partnerships with galleries and artists worldwide, making it a reputable source for high-quality art. Artsy, on the other hand, is an online platform that connects artists with collectors and galleries. It offers a vast collection of paintings, drawings, and sculptures from both emerging and established artists.

In conclusion, Etsy, eBay, Saatchi Art, and Artsy are the leading websites where artists can sell paintings in the United States. Each platform has its unique strengths, but they all share the common goal of connecting artists with potential buyers. The choice of platform will depend on the artist's specific needs, such as the type of artwork they produce, their target audience, and their preferred selling methods.