Description

Based on the search results, while many vitamin C serums are available in 30ml or 50ml bottles, the most suitable options for oily skin that provide a lightweight, non-sticky, and brightening experience are often 10% to 15% concentration formulas. 
Here is a detailed description of top-rated Vitamin C serums for oily skin, which can be found in various sizes:

1. Deconstruct 10% Vitamin C Serum (Best for Beginner Oily Skin) 
Description: A non-irritating, water-based, and lightweight formulation containing 10% Vitamin C and 0.5% Ferulic Acid. It is designed to brighten dull skin, reduce tanning, and control pigmentation.
Key Benefit for Oily Skin: Its non-sticky texture is ideal for oily and acne-prone skin, as it prevents clogging of pores while promoting even-toned skin.
Key Ingredients: 3-O-Ethyl Ascorbic Acid (stable Vitamin C) and Ferulic Acid. 

2. Plum 15% Vitamin C Advanced Serum (Best for Fast Results) 
Description: A potent 15% Ethyl Ascorbic Acid serum infused with Mandarin and Kakadu Plum. It is vegan, fragrance-free, and designed to fight pigmentation and dark spots.
Key Benefit for Oily Skin: The quick-absorbing, liquid formula is non-sticky and provides a radiant finish without adding excess oil. 

3. Garnier Bright Complete 30X Vitamin C Booster Serum (Best Drugstore Option) 
Description: Contains 30x Pure Vitamin C and lemon extract to brighten skin instantly and reduce dark spots and acne marks.
Key Benefit for Oily Skin: Known for its extremely lightweight, non-greasy formula that penetrates the skin immediately, leaving it fresh and non-sticky. 

4. La Roche-Posay Pure 12% Vitamin C Oil Control Serum (Best Premium Option) 
Description: A highly concentrated serum (12% Vitamin C) designed specifically for oily and combination skin.
Key Benefit for Oily Skin: Formulated with Salicylic Acid to unclog pores and Vitamin C Guard technology to reduce oil, enhance radiance, and smooth fine lines.