Head-to-Head Comparison

Updated September 5, 2026

Bulova Classic Automatic 98A139 vs Casio G-Shock GA-B2100 CasiOak

Bulova's timepiece meets Casio's diver

Quick Verdict

The Casio G-Shock GA-B2100 CasiOak ($100–$150) delivers Casio Quartz (Solar-Powered) technology in the tier below the Bulova Classic Automatic 98A139 ($250–$500). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Classic Automatic 98A139 justifies its premium with Japanese Movement heritage and Automatic, 21 Jewels. Both represent excellent choices in the luxury watch category.

BulovaClassic Automatic 98A139$250–$500 Check price CasioG-Shock GA-B2100 CasiOak$100–$150 Check price

Transparency — We earn a small commission on purchases made through our Amazon links. This doesn't affect our editorial independence.

Bulova

Classic Automatic 98A139

$250–$500

Check Price Full Review

Casio

G-Shock GA-B2100 CasiOak

$100–$150

Check Price Full Review

Specifications Compared

Feature	Bulova Classic Automatic 98A139	Casio G-Shock GA-B2100 CasiOak
Price	$250–$500	$100–$150
Case Size	45mm	45.4mm (48.5mm lug-to-lug, 11.9mm thick)
Movement	Automatic, 21 Jewels	Quartz Module 5689 (Tough Solar + Bluetooth)
Caliber Type	Self-Winding Automatic	Casio Quartz (Solar-Powered)
Power Reserve	—	About 7 months on a full charge without light; about 18 months in power-saving (Casio)
Water Resistance	30m (3 ATM)	200m (20 ATM)
Crystal	Domed Crystal	Mineral Glass
Case Material	Black Ion-Plated Stainless Steel	Carbon Core Guard Resin
Origin	Japanese Movement	Made in Japan

Category-by-Category Analysis

🎨

Design & Aesthetics

Edge: Draw

Bulova's design language vs Casio's approach

The Bulova Classic Automatic 98A139 features a Black Ion-Plated Stainless Steel case at 45mm with Domed Crystal protection. The Casio G-Shock GA-B2100 CasiOak offers Carbon Core Guard Resin construction at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with Mineral Glass. Both represent their brand's distinct design philosophy and heritage.

⚙️

Movement & Performance

Edge: Casio

Automatic, 21 Jewels vs Quartz Module 5689 (Tough Solar + Bluetooth)

The Classic Automatic 98A139 runs the Automatic, 21 Jewels (Self-Winding Automatic, standard power reserve) at standard frequency. The G-Shock GA-B2100 CasiOak uses the Quartz Module 5689 (Tough Solar + Bluetooth) (Casio Quartz (Solar-Powered), About 7 months on a full charge without light; about 18 months in power-saving (Casio) reserve) at standard. The G-Shock GA-B2100 CasiOak offers a longer power reserve.

📏

Wearability & Fit

Edge: Bulova

45mm vs 45.4mm (48.5mm lug-to-lug, 11.9mm thick) — different wrist presence

At 45mm, the Classic Automatic 98A139 wears more compactly on smaller wrists compared to the G-Shock GA-B2100 CasiOak at 45.4mm (48.5mm lug-to-lug, 11.9mm thick). Water resistance differs: 30m (3 ATM) vs 200m (20 ATM).

💰

Value & Cost of Ownership

Edge: Casio

Casio sits in the lower tier

The Bulova Classic Automatic 98A139 sits at $250–$500 and the Casio G-Shock GA-B2100 CasiOak at $100–$150. On the specs that outlast any price: the Classic Automatic 98A139 uses Domed Crystal with a standard reserve, against Mineral Glass and About 7 months on a full charge without light; about 18 months in power-saving (Casio) on the G-Shock GA-B2100 CasiOak. Service intervals are typically 5-7 years for both.

💧

Water Resistance

Edge: Casio

30m (3 ATM) vs 200m (20 ATM)

The Classic Automatic 98A139 is rated to 30m (3 ATM) while the G-Shock GA-B2100 CasiOak handles 200m (20 ATM). The G-Shock GA-B2100 CasiOak offers superior water resistance.

Our Verdict

Bulova

Classic Automatic 98A139

Choose the Bulova Classic Automatic 98A139 if you prioritize Self-Winding Automatic engineering, Japanese Movement craftsmanship, and 30m (3 ATM) water resistance. At $250–$500, it delivers Automatic, 21 Jewels with solid power reserve.

Check Price on Amazon

Casio

G-Shock GA-B2100 CasiOak

Choose the Casio G-Shock GA-B2100 CasiOak if you value Casio Quartz (Solar-Powered) technology, Made in Japan heritage, and 45.4mm (48.5mm lug-to-lug, 11.9mm thick) proportions. At $100–$150, the Quartz Module 5689 (Tough Solar + Bluetooth) with About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve makes it a compelling choice.

Check Price on Amazon

Try Prime Free — Free Shipping on Both Watches Students & 18–24: start Prime for Young Adults free

The Bottom Line

The Bulova Classic Automatic 98A139 and Casio G-Shock GA-B2100 CasiOak represent two distinct approaches to fine watchmaking — the Bulova bringing Japanese Movement tradition while Casio delivers Made in Japan engineering.

Frequently Asked Questions

The Bulova Classic Automatic 98A139 is the better buy if you want a mechanical movement; the Casio G-Shock GA-B2100 CasiOak is the better buy if you want solar power and quartz accuracy with no servicing. For water, the Casio G-Shock GA-B2100 CasiOak is rated 200 m against 30 m, which is the difference between swimming and diving on one side and splashes on the other. On price, the Casio G-Shock GA-B2100 CasiOak sits a band lower ($100–$150 against $250–$500), so it is the cheaper way into the category. Neither is better at everything; the spec table above shows movement, case size, water resistance and crystal side by side so you can weigh what matters to you. We do not test units, so this is the makers' data, not a bench result.

The Casio G-Shock GA-B2100 CasiOak offers better upfront value, sitting a tier lower at $100–$150. However, the Bulova Classic Automatic 98A139 may justify its premium with superior finishing, heritage, or resale value.

Both are suitable for daily wear. The Classic Automatic 98A139 at 45mm with 30m (3 ATM) water resistance handles everyday situations. The G-Shock GA-B2100 CasiOak at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with 200m (20 ATM) is similarly capable. The Classic Automatic 98A139 uses Domed Crystal while the G-Shock GA-B2100 CasiOak uses Mineral Glass.

More Comparisons

Seiko Prospex Turtle vs G-Shock CasiOak

Mechanical dive heritage vs digital indestructibility

Citizen Tsuyosa vs G-Shock CasiOak

The classy one and the sporty one

G-Shock CasiOak vs G-Shock DW-5600

Octagonal analogue-digital or the original square

Explore These Watches

Bulova Classic Automatic 98A139 — Full Review Casio G-Shock GA-B2100 CasiOak — Full Review Browse All Guides

How This Page Was Made

Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.